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* irq_work: Add generic hardirq context callbacksPeter Zijlstra2010-10-181-2/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Provide a mechanism that allows running code in IRQ context. It is most useful for NMI code that needs to interact with the rest of the system -- like wakeup a task to drain buffers. Perf currently has such a mechanism, so extract that and provide it as a generic feature, independent of perf so that others may also benefit. The IRQ context callback is generated through self-IPIs where possible, or on architectures like powerpc the decrementer (the built-in timer facility) is set to generate an interrupt immediately. Architectures that don't have anything like this get to do with a callback from the timer tick. These architectures can call irq_work_run() at the tail of any IRQ handlers that might enqueue such work (like the perf IRQ handler) to avoid undue latencies in processing the work. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Kyle McMartin <kyle@mcmartin.ca> Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com> [ various fixes ] Signed-off-by: Huang Ying <ying.huang@intel.com> LKML-Reference: <1287036094.7768.291.camel@yhuang-dev> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* kernel/timer.c: fix kernel-doc function parameter warningRandy Dunlap2010-08-101-0/+1
| | | | | | | | | | Fix kernel-doc warning, add @timer description: Warning(kernel/timer.c:335): No description found for parameter 'timer' Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Merge branch 'timers-for-linus' of ↵Linus Torvalds2010-08-061-2/+29
|\ | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: Documentation: Add timers/timers-howto.txt timer: Added usleep_range timer Revert "timer: Added usleep[_range] timer" clockevents: Remove the per cpu tick skew posix_timer: Move copy_to_user(created_timer_id) down in timer_create() timer: Added usleep[_range] timer timers: Document meaning of deferrable timer
| * timer: Added usleep_range timerPatrick Pannuto2010-08-041-0/+22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | usleep_range is a finer precision implementations of msleep and is designed to be a drop-in replacement for udelay where a precise sleep / busy-wait is unnecessary. Since an easy interface to hrtimers could lead to an undesired proliferation of interrupts, we provide only a "range" API, forcing the caller to think about an acceptable tolerance on both ends and hopefully avoiding introducing another interrupt. INTRO As discussed here ( http://lkml.org/lkml/2007/8/3/250 ), msleep(1) is not precise enough for many drivers (yes, sleep precision is an unfair notion, but consistently sleeping for ~an order of magnitude greater than requested is worth fixing). This patch adds a usleep API so that udelay does not have to be used. Obviously not every udelay can be replaced (those in atomic contexts or being used for simple bitbanging come to mind), but there are many, many examples of mydriver_write(...) /* Wait for hardware to latch */ udelay(100) in various drivers where a busy-wait loop is neither beneficial nor necessary, but msleep simply does not provide enough precision and people are using a busy-wait loop instead. CONCERNS FROM THE RFC Why is udelay a problem / necessary? Most callers of udelay are in device/ driver initialization code, which is serial... As I see it, there is only benefit to sleeping over a delay; the notion of "refactoring" areas that use udelay was presented, but I see usleep as the refactoring. Consider i2c, if the bus is busy, you need to wait a bit (say 100us) before trying again, your current options are: * udelay(100) * msleep(1) <-- As noted above, actually as high as ~20ms on some platforms, so not really an option * Manually set up an hrtimer to try again in 100us (which is what usleep does anyway...) People choose the udelay route because it is EASY; we need to provide a better easy route. Device / driver / boot code is *currently* serial, but every few months someone makes noise about parallelizing boot, and IMHO, a little forward-thinking now is one less thing to worry about if/when that ever happens udelay's could be preempted Sure, but if udelay plans on looping 1000 times, and it gets preempted on loop 200, whenever it's scheduled again, it is going to do the next 800 loops. Is the interruptible case needed? Probably not, but I see usleep as a very logical parallel to msleep, so it made sense to include the "full" API. Processors are getting faster (albeit not as quickly as they are becoming more parallel), so if someone wanted to be interruptible for a few usecs, why not let them? If this is a contentious point, I'm happy to remove it. OTHER THOUGHTS I believe there is also value in exposing the usleep_range option; it gives the scheduler a lot more flexibility and allows the programmer to express his intent much more clearly; it's something I would hope future driver writers will take advantage of. To get the results in the NUMBERS section below, I literally s/udelay/usleep the kernel tree; I had to go in and undo the changes to the USB drivers, but everything else booted successfully; I find that extremely telling in and of itself -- many people are using a delay API where a sleep will suit them just fine. SOME ATTEMPTS AT NUMBERS It turns out that calculating quantifiable benefit on this is challenging, so instead I will simply present the current state of things, and I hope this to be sufficient: How many udelay calls are there in 2.6.35-rc5? udealy(ARG) >= | COUNT 1000 | 319 500 | 414 100 | 1146 20 | 1832 I am working on Android, so that is my focus for this. The following table is a modified usleep that simply printk's the amount of time requested to sleep; these tests were run on a kernel with udelay >= 20 --> usleep "boot" is power-on to lock screen "power collapse" is when the power button is pushed and the device suspends "resume" is when the power button is pushed and the lock screen is displayed (no touchscreen events or anything, just turning on the display) "use device" is from the unlock swipe to clicking around a bit; there is no sd card in this phone, so fail loading music, video, camera ACTION | TOTAL NUMBER OF USLEEP CALLS | NET TIME (us) boot | 22 | 1250 power-collapse | 9 | 1200 resume | 5 | 500 use device | 59 | 7700 The most interesting category to me is the "use device" field; 7700us of busy-wait time that could be put towards better responsiveness, or at the least less power usage. Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org> Cc: apw@canonical.com Cc: corbet@lwn.net Cc: arjan@linux.intel.com Cc: Randy Dunlap <rdunlap@xenotime.net> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * Revert "timer: Added usleep[_range] timer"Thomas Gleixner2010-08-041-22/+0
| | | | | | | | | | | | | | This reverts commit 22b8f15c2f7130bb0386f548428df2ffd4e81903 to merge an advanced version. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * timer: Added usleep[_range] timerPatrick Pannuto2010-07-231-0/+22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | usleep[_range] are finer precision implementations of msleep and are designed to be drop-in replacements for udelay where a precise sleep / busy-wait is unnecessary. They also allow an easy interface to specify slack when a precise (ish) wakeup is unnecessary to help minimize wakeups Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org> Cc: akinobu.mita@gmail.com Cc: sboyd@codeaurora.org Acked-by: Arjan van de Ven <arjan@linux.intel.com> LKML-Reference: <4C44CDD2.1070708@codeaurora.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * timers: Document meaning of deferrable timerJ. Bruce Fields2010-07-231-2/+7
| | | | | | | | | | | | | | | | | | | | | | Steal some text from 6e453a67510 "Add support for deferrable timers". A reader shouldn't have to dig through the git logs for the basic description of a deferrable timer. Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu> Cc: johnstul@us.ibm.com Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | Merge branch 'sched-core-for-linus' of ↵Linus Torvalds2010-08-061-6/+2
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (27 commits) sched: Use correct macro to display sched_child_runs_first in /proc/sched_debug sched: No need for bootmem special cases sched: Revert nohz_ratelimit() for now sched: Reduce update_group_power() calls sched: Update rq->clock for nohz balanced cpus sched: Fix spelling of sibling sched, cpuset: Drop __cpuexit from cpu hotplug callbacks sched: Fix the racy usage of thread_group_cputimer() in fastpath_timer_check() sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand() sched: thread_group_cputime: Simplify, document the "alive" check sched: Remove the obsolete exit_state/signal hacks sched: task_tick_rt: Remove the obsolete ->signal != NULL check sched: __sched_setscheduler: Read the RLIMIT_RTPRIO value lockless sched: Fix comments to make them DocBook happy sched: Fix fix_small_capacity powerpc: Exclude arch_sd_sibiling_asym_packing() on UP powerpc: Enable asymmetric SMT scheduling on POWER7 sched: Add asymmetric group packing option for sibling domain sched: Fix capacity calculations for SMT4 sched: Change nohz idle load balancing logic to push model ...
| * | sched: Change nohz idle load balancing logic to push modelVenkatesh Pallipadi2010-06-091-6/+2
| |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In the new push model, all idle CPUs indeed go into nohz mode. There is still the concept of idle load balancer (performing the load balancing on behalf of all the idle cpu's in the system). Busy CPU kicks the nohz balancer when any of the nohz CPUs need idle load balancing. The kickee CPU does the idle load balancing on behalf of all idle CPUs instead of the normal idle balance. This addresses the below two problems with the current nohz ilb logic: * the idle load balancer continued to have periodic ticks during idle and wokeup frequently, even though it did not have any rebalancing to do on behalf of any of the idle CPUs. * On x86 and CPUs that have APIC timer stoppage on idle CPUs, this periodic wakeup can result in a periodic additional interrupt on a CPU doing the timer broadcast. Also currently we are migrating the unpinned timers from an idle to the cpu doing idle load balancing (when all the cpus in the system are idle, there is no idle load balancing cpu and timers get added to the same idle cpu where the request was made. So the existing optimization works only on semi idle system). And In semi idle system, we no longer have periodic ticks on the idle load balancer CPU. Using that cpu will add more delays to the timers than intended (as that cpu's timer base may not be uptodate wrt jiffies etc). This was causing mysterious slowdowns during boot etc. For now, in the semi idle case, use the nearest busy cpu for migrating timers from an idle cpu. This is good for power-savings anyway. Signed-off-by: Venkatesh Pallipadi <venki@google.com> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Gleixner <tglx@linutronix.de> LKML-Reference: <1274486981.2840.46.camel@sbs-t61.sc.intel.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* | Merge branch 'perf-core-for-linus' of ↵Linus Torvalds2010-08-061-1/+0
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (162 commits) tracing/kprobes: unregister_trace_probe needs to be called under mutex perf: expose event__process function perf events: Fix mmap offset determination perf, powerpc: fsl_emb: Restore setting perf_sample_data.period perf, powerpc: Convert the FSL driver to use local64_t perf tools: Don't keep unreferenced maps when unmaps are detected perf session: Invalidate last_match when removing threads from rb_tree perf session: Free the ref_reloc_sym memory at the right place x86,mmiotrace: Add support for tracing STOS instruction perf, sched migration: Librarize task states and event headers helpers perf, sched migration: Librarize the GUI class perf, sched migration: Make the GUI class client agnostic perf, sched migration: Make it vertically scrollable perf, sched migration: Parameterize cpu height and spacing perf, sched migration: Fix key bindings perf, sched migration: Ignore unhandled task states perf, sched migration: Handle ignored migrate out events perf: New migration tool overview tracing: Drop cpparg() macro perf: Use tracepoint_synchronize_unregister() to flush any pending tracepoint call ... Fix up trivial conflicts in Makefile and drivers/cpufreq/cpufreq.c
| * \ Merge branch 'perf/nmi' into perf/coreIngo Molnar2010-08-051-1/+0
| |\ \ | | |/ | |/| | | | | | | | | | | | | | | | | | | Conflicts: kernel/Makefile Merge reason: Add the now complete topic, fix the conflict. Signed-off-by: Ingo Molnar <mingo@elte.hu>
| | * lockup_detector: Touch_softlockup cleanups and softlockup_tick removalDon Zickus2010-05-121-1/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Just some code cleanup to make touch_softlockup clearer and remove the softlockup_tick function as it is no longer needed. Also remove the /proc softlockup_thres call as it has been changed to watchdog_thres. Signed-off-by: Don Zickus <dzickus@redhat.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Cyrill Gorcunov <gorcunov@gmail.com> Cc: Eric Paris <eparis@redhat.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> LKML-Reference: <1273266711-18706-3-git-send-email-dzickus@redhat.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
* | | timer: add on-stack deferrable timer interfacesJesse Barnes2010-08-031-0/+13
|/ / | | | | | | | | | | | | | | | | In some cases (for instance with kernel threads) it may be desireable to use on-stack deferrable timers to get their power saving benefits. Add interfaces to support this for the IPS driver. Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Matthew Garrett <mjg@redhat.com>
* | kernel/: fix BUG_ON checks for cpu notifier callbacks direct callAkinobu Mita2010-06-041-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The commit 80b5184cc537718122e036afe7e62d202b70d077 ("kernel/: convert cpu notifier to return encapsulate errno value") changed the return value of cpu notifier callbacks. Those callbacks don't return NOTIFY_BAD on failures anymore. But there are a few callbacks which are called directly at init time and checking the return value. I forgot to change BUG_ON checking by the direct callers in the commit. Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* | Merge branch 'timers-fixes-for-linus' of ↵Linus Torvalds2010-05-281-3/+7
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: posix_timer: Fix error path in timer_create hrtimer: Avoid double seqlock timers: Move local variable into else section timers: Fix slack calculation really
| * | timers: Move local variable into else sectionThomas Gleixner2010-05-261-2/+3
| | | | | | | | | | | | | | | | | | Fix nit-picking coding style detail. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * | timers: Fix slack calculation reallyThomas Gleixner2010-05-251-5/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | commit f00e047ef (timers: Fix slack calculation for expired timers) fixed the issue of slack on expired timers only partially. Linus noticed that jiffies is volatile so it is reloaded twice, which generates bad code. But its worse. This can defeat the time_after() check if jiffies are incremented between time_after() and the slack calculation. Fix it by reading jiffies into a local variable, which prevents the compiler from loading it twice. While at it make the > -1 check into >= 0 which is easier to read. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org>
* | | kernel/: convert cpu notifier to return encapsulate errno valueAkinobu Mita2010-05-271-2/+5
|/ / | | | | | | | | | | | | | | | | | | | | By the previous modification, the cpu notifier can return encapsulate errno value. This converts the cpu notifiers for kernel/*.c Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* | timers: Fix slack calculation for expired timersJeff Chua2010-05-241-3/+4
| | | | | | | | | | | | | | | | | | | | | | commit 3bbb9ec946 (timers: Introduce the concept of timer slack for legacy timers) does not take the case into account when the timer is already expired. This broke wireless drivers. The solution is not to apply slack to already expired timers. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Arjan van de Ven <arjan@linux.intel.com>
* | Merge branch 'linus' into timers/coreThomas Gleixner2010-05-101-0/+2
|\ \ | |/ | | | | | | | | Reason: Further posix_cpu_timer patches depend on mainline changes Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * include cleanup: Update gfp.h and slab.h includes to prepare for breaking ↵Tejun Heo2010-03-301-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | implicit slab.h inclusion from percpu.h percpu.h is included by sched.h and module.h and thus ends up being included when building most .c files. percpu.h includes slab.h which in turn includes gfp.h making everything defined by the two files universally available and complicating inclusion dependencies. percpu.h -> slab.h dependency is about to be removed. Prepare for this change by updating users of gfp and slab facilities include those headers directly instead of assuming availability. As this conversion needs to touch large number of source files, the following script is used as the basis of conversion. http://userweb.kernel.org/~tj/misc/slabh-sweep.py The script does the followings. * Scan files for gfp and slab usages and update includes such that only the necessary includes are there. ie. if only gfp is used, gfp.h, if slab is used, slab.h. * When the script inserts a new include, it looks at the include blocks and try to put the new include such that its order conforms to its surrounding. It's put in the include block which contains core kernel includes, in the same order that the rest are ordered - alphabetical, Christmas tree, rev-Xmas-tree or at the end if there doesn't seem to be any matching order. * If the script can't find a place to put a new include (mostly because the file doesn't have fitting include block), it prints out an error message indicating which .h file needs to be added to the file. The conversion was done in the following steps. 1. The initial automatic conversion of all .c files updated slightly over 4000 files, deleting around 700 includes and adding ~480 gfp.h and ~3000 slab.h inclusions. The script emitted errors for ~400 files. 2. Each error was manually checked. Some didn't need the inclusion, some needed manual addition while adding it to implementation .h or embedding .c file was more appropriate for others. This step added inclusions to around 150 files. 3. The script was run again and the output was compared to the edits from #2 to make sure no file was left behind. 4. Several build tests were done and a couple of problems were fixed. e.g. lib/decompress_*.c used malloc/free() wrappers around slab APIs requiring slab.h to be added manually. 5. The script was run on all .h files but without automatically editing them as sprinkling gfp.h and slab.h inclusions around .h files could easily lead to inclusion dependency hell. Most gfp.h inclusion directives were ignored as stuff from gfp.h was usually wildly available and often used in preprocessor macros. Each slab.h inclusion directive was examined and added manually as necessary. 6. percpu.h was updated not to include slab.h. 7. Build test were done on the following configurations and failures were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my distributed build env didn't work with gcov compiles) and a few more options had to be turned off depending on archs to make things build (like ipr on powerpc/64 which failed due to missing writeq). * x86 and x86_64 UP and SMP allmodconfig and a custom test config. * powerpc and powerpc64 SMP allmodconfig * sparc and sparc64 SMP allmodconfig * ia64 SMP allmodconfig * s390 SMP allmodconfig * alpha SMP allmodconfig * um on x86_64 SMP allmodconfig 8. percpu.h modifications were reverted so that it could be applied as a separate patch and serve as bisection point. Given the fact that I had only a couple of failures from tests on step 6, I'm fairly confident about the coverage of this conversion patch. If there is a breakage, it's likely to be something in one of the arch headers which should be easily discoverable easily on most builds of the specific arch. Signed-off-by: Tejun Heo <tj@kernel.org> Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
| * timer stats: Fix del_timer_sync() and try_to_del_timer_sync()Andrew Morton2010-03-121-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | These functions forgot to run timer_stats_timer_clear_start_info(). It's unobvious what effect this has and whether it matters much - we won't be printing it out anyway if the timer's detached. Untested, just an Ingo trollpatch. [ Nevertheless correct - tglx ] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: johnstul@us.ibm.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | timers: Introduce the concept of timer slack for legacy timersArjan van de Ven2010-04-061-0/+56
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | While HR timers have had the concept of timer slack for quite some time now, the legacy timers lacked this concept, and had to make do with round_jiffies() and friends. Timer slack is important for power management; grouping timers reduces the number of wakeups which in turn reduces power consumption. This patch introduces timer slack to the legacy timers using the following pieces: * A slack field in the timer struct * An api (set_timer_slack) that callers can use to set explicit timer slack * A default slack of 0.4% of the requested delay for callers that do not set any explicit slack * Rounding code that is part of mod_timer() that tries to group timers around jiffies values every 'power of two' (so quick timers will group around every 2, but longer timers will group around every 4, 8, 16, 32 etc) Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> Cc: johnstul@us.ibm.com Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | timer: Try to survive timer callback preempt_count leakThomas Gleixner2010-03-121-3/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If a timer callback leaks preempt_count we currently assert a BUG(). That makes it unnecessarily hard to retrieve information about the problem especially on laptops and headless stations. There is a decent chance to survive the preempt_count leak by restoring the preempt_count to the value before the callback. That allows in many cases to get valuable information about the root cause of the problem. We carried that fixup in preempt-rt for years and were able to decode such wreckage quite a few times. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Linux Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arjan van de Veen <arjan@infradead.org>
* | timer: Split out timer function callThomas Gleixner2010-03-121-36/+36
| | | | | | | | | | | | | | The ident level is starting to be annoying. More white space than actual code. Split out the timer function call into its own function. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | timer: Print function name for timer callbacks modifying preemption countUwe Kleine-König2010-03-121-5/+2
|/ | | | | | | | | | | | | | | A function scheduled with a timer must not exit with a different preempt count than it was entered. To make helping users running into the corresponding BUG() easier also print the name of the bad function not only its address. [ tglx: Sanitized printk ] Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Cc: johnstul@us.ibm.com Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* perf: Fix perf_event_do_pending() fallback callsitePeter Zijlstra2010-01-211-2/+1
| | | | | | | | | | | | | Paul questioned the context in which we should call perf_event_do_pending(). After looking at that I found that it should be called from IRQ context these days, however the fallback call-site is placed in softirq context. Ammend this by placing the callback in the IRQ timer path. Reported-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1263374859.4244.192.camel@laptop> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* timers: Remove duplicate setting of new_base in __mod_timer()Simon Horman2009-12-171-2/+0
| | | | | | | | | | new_base is set using per_cpu(tvec_bases, cpu) after selecting the desired value of cpu immediately below so this line is a unnecessary. Signed-off-by: Simon Horman <horms@verge.net.au> LKML-Reference: <20091217001542.GD25317@verge.net.au> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* Merge branch 'timers-for-linus' of ↵Linus Torvalds2009-09-231-4/+28
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: itimers: Add tracepoints for itimer hrtimer: Add tracepoint for hrtimers timers: Add tracepoints for timer_list timers cputime: Optimize jiffies_to_cputime(1) itimers: Simplify arm_timer() code a bit itimers: Fix periodic tics precision itimers: Merge ITIMER_VIRT and ITIMER_PROF Trivial header file include conflicts in kernel/fork.c
| * timers: Add tracepoints for timer_list timersXiao Guangrong2009-08-291-4/+28
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Add tracepoints which cover the timer life cycle. The tracepoints are integrated with the already existing debug_object debug points as far as possible. Based on patches from Mathieu: http://marc.info/?l=linux-kernel&m=123791201816247&w=2 and Anton: http://marc.info/?l=linux-kernel&m=124331396919301&w=2 [ tglx: Fixed timeout value in timer_start tracepoint, massaged comments and made the printk's more readable ] Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> Cc: Anton Blanchard <anton@samba.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: Peter Zijlstra <peterz@infradead.org> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Zhaolei <zhaolei@cn.fujitsu.com> LKML-Reference: <4A7F8A9B.3040201@cn.fujitsu.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | perf: Do the big rename: Performance Counters -> Performance EventsIngo Molnar2009-09-211-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Bye-bye Performance Counters, welcome Performance Events! In the past few months the perfcounters subsystem has grown out its initial role of counting hardware events, and has become (and is becoming) a much broader generic event enumeration, reporting, logging, monitoring, analysis facility. Naming its core object 'perf_counter' and naming the subsystem 'perfcounters' has become more and more of a misnomer. With pending code like hw-breakpoints support the 'counter' name is less and less appropriate. All in one, we've decided to rename the subsystem to 'performance events' and to propagate this rename through all fields, variables and API names. (in an ABI compatible fashion) The word 'event' is also a bit shorter than 'counter' - which makes it slightly more convenient to write/handle as well. Thanks goes to Stephane Eranian who first observed this misnomer and suggested a rename. User-space tooling and ABI compatibility is not affected - this patch should be function-invariant. (Also, defconfigs were not touched to keep the size down.) This patch has been generated via the following script: FILES=$(find * -type f | grep -vE 'oprofile|[^K]config') sed -i \ -e 's/PERF_EVENT_/PERF_RECORD_/g' \ -e 's/PERF_COUNTER/PERF_EVENT/g' \ -e 's/perf_counter/perf_event/g' \ -e 's/nb_counters/nb_events/g' \ -e 's/swcounter/swevent/g' \ -e 's/tpcounter_event/tp_event/g' \ $FILES for N in $(find . -name perf_counter.[ch]); do M=$(echo $N | sed 's/perf_counter/perf_event/g') mv $N $M done FILES=$(find . -name perf_event.*) sed -i \ -e 's/COUNTER_MASK/REG_MASK/g' \ -e 's/COUNTER/EVENT/g' \ -e 's/\<event\>/event_id/g' \ -e 's/counter/event/g' \ -e 's/Counter/Event/g' \ $FILES ... to keep it as correct as possible. This script can also be used by anyone who has pending perfcounters patches - it converts a Linux kernel tree over to the new naming. We tried to time this change to the point in time where the amount of pending patches is the smallest: the end of the merge window. Namespace clashes were fixed up in a preparatory patch - and some stylistic fallout will be fixed up in a subsequent patch. ( NOTE: 'counters' are still the proper terminology when we deal with hardware registers - and these sed scripts are a bit over-eager in renaming them. I've undone some of that, but in case there's something left where 'counter' would be better than 'event' we can undo that on an individual basis instead of touching an otherwise nicely automated patch. ) Suggested-by: Stephane Eranian <eranian@google.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Paul Mackerras <paulus@samba.org> Reviewed-by: Arjan van de Ven <arjan@linux.intel.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: David Howells <dhowells@redhat.com> Cc: Kyle McMartin <kyle@mcmartin.ca> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: <linux-arch@vger.kernel.org> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* | Merge branch 'timers-for-linus' of ↵Linus Torvalds2009-09-181-3/+25
|\ \ | |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (34 commits) time: Prevent 32 bit overflow with set_normalized_timespec() clocksource: Delay clocksource down rating to late boot clocksource: clocksource_select must be called with mutex locked clocksource: Resolve cpu hotplug dead lock with TSC unstable, fix crash timers: Drop a function prototype clocksource: Resolve cpu hotplug dead lock with TSC unstable timer.c: Fix S/390 comments timekeeping: Fix invalid getboottime() value timekeeping: Fix up read_persistent_clock() breakage on sh timekeeping: Increase granularity of read_persistent_clock(), build fix time: Introduce CLOCK_REALTIME_COARSE x86: Do not unregister PIT clocksource on PIT oneshot setup/shutdown clocksource: Avoid clocksource watchdog circular locking dependency clocksource: Protect the watchdog rating changes with clocksource_mutex clocksource: Call clocksource_change_rating() outside of watchdog_lock timekeeping: Introduce read_boot_clock timekeeping: Increase granularity of read_persistent_clock() timekeeping: Update clocksource with stop_machine timekeeping: Add timekeeper read_clock helper functions timekeeping: Move NTP adjusted clock multiplier to struct timekeeper ... Fix trivial conflict due to MIPS lemote -> loongson renaming.
| * timer.c: Fix S/390 commentsRandy Dunlap2009-08-261-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | Fix typos and add omitted words. Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: akpm <akpm@linux-foundation.org> Cc: linux390@de.ibm.com Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> LKML-Reference: <20090825143541.43fc2ed8.randy.dunlap@oracle.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
| * Merge branch 'linus' into timers/coreThomas Gleixner2009-08-141-1/+1
| |\ | | | | | | | | | | | | | | | | | | Reason: Martin's timekeeping cleanup series depends on both timers/core and mainline changes. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * | timers: Cache __next_timer_interrupt resultMartin Schwidefsky2009-08-041-1/+23
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Each time a cpu goes to sleep on a NOHZ=y system the timer wheel is searched for the next timer interrupt. It can take quite a few cycles to find the next pending timer. This patch adds a field to tvec_base that caches the result of __next_timer_interrupt. The hit ratio is around 80% on my thinkpad under normal use, on a server I've seen hit ratios from 5% to 95% dependent on the workload. -v2: jiffies wrap fixes Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: john stultz <johnstul@us.ibm.com> Cc: Venki Pallipadi <venkatesh.pallipadi@intel.com> LKML-Reference: <20090721202505.7d56a079@skybase> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* | | rcu: Simplify rcu_pending()/rcu_check_callbacks() APIPaul E. McKenney2009-08-231-2/+1
| |/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | All calls from outside RCU are of the form: if (rcu_pending(cpu)) rcu_check_callbacks(cpu, user); This is silly, instead we put a call to rcu_pending() in rcu_check_callbacks(), and then make the outside calls be to rcu_check_callbacks(). This cuts down on the code a bit and also gives the compiler a better chance of optimizing. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josht@linux.vnet.ibm.com Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org LKML-Reference: <125097461311-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* | timer: Avoid reading uninitialized dataPavel Roskin2009-07-181-1/+1
|/ | | | | | | | | timer->expires may be uninitialized, so check timer_pending() before touching timer->expires to pacify kmemcheck. Signed-off-by: Pavel Roskin <proski@gnu.org> LKML-Reference: <20090718204602.5191.360.stgit@mj.roinet.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* timer stats: Optimize by adding quick check to avoid function callsHeiko Carstens2009-06-241-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | When the kernel is configured with CONFIG_TIMER_STATS but timer stats are runtime disabled we still get calls to __timer_stats_timer_set_start_info which initializes some fields in the corresponding struct timer_list. So add some quick checks in the the timer stats setup functions to avoid function calls to __timer_stats_timer_set_start_info when timer stats are disabled. In an artificial workload that does nothing but playing ping pong with a single tcp packet via loopback this decreases cpu consumption by 1 - 1.5%. This is part of a modified function trace output on SLES11: perl-2497 [00] 28630647177732388 [+ 125]: sk_reset_timer <-tcp_v4_rcv perl-2497 [00] 28630647177732513 [+ 125]: mod_timer <-sk_reset_timer perl-2497 [00] 28630647177732638 [+ 125]: __timer_stats_timer_set_start_info <-mod_timer perl-2497 [00] 28630647177732763 [+ 125]: __mod_timer <-mod_timer perl-2497 [00] 28630647177732888 [+ 125]: __timer_stats_timer_set_start_info <-__mod_timer perl-2497 [00] 28630647177733013 [+ 93]: lock_timer_base <-__mod_timer Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Mustafa Mesanovic <mustafa.mesanovic@de.ibm.com> Cc: Arjan van de Ven <arjan@infradead.org> LKML-Reference: <20090623153811.GA4641@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* Merge branch 'timers-for-linus-migration' of ↵Linus Torvalds2009-06-151-7/+44
|\ | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'timers-for-linus-migration' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: timers: Logic to move non pinned timers timers: /proc/sys sysctl hook to enable timer migration timers: Identifying the existing pinned timers timers: Framework for identifying pinned timers timers: allow deferrable timers for intervals tv2-tv5 to be deferred Fix up conflicts in kernel/sched.c and kernel/timer.c manually
| * timers: Logic to move non pinned timersArun R Bharadwaj2009-05-131-3/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | * Arun R Bharadwaj <arun@linux.vnet.ibm.com> [2009-04-16 12:11:36]: This patch migrates all non pinned timers and hrtimers to the current idle load balancer, from all the idle CPUs. Timers firing on busy CPUs are not migrated. While migrating hrtimers, care should be taken to check if migrating a hrtimer would result in a latency or not. So we compare the expiry of the hrtimer with the next timer interrupt on the target cpu and migrate the hrtimer only if it expires *after* the next interrupt on the target cpu. So, added a clockevents_get_next_event() helper function to return the next_event on the target cpu's clock_event_device. [ tglx: cleanups and simplifications ] Signed-off-by: Arun R Bharadwaj <arun@linux.vnet.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * timers: Framework for identifying pinned timersArun R Bharadwaj2009-05-131-4/+27
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | * Arun R Bharadwaj <arun@linux.vnet.ibm.com> [2009-04-16 12:11:36]: This patch creates a new framework for identifying cpu-pinned timers and hrtimers. This framework is needed because pinned timers are expected to fire on the same CPU on which they are queued. So it is essential to identify these and not migrate them, in case there are any. For regular timers, the currently existing add_timer_on() can be used queue pinned timers and subsequently mod_timer_pinned() can be used to modify the 'expires' field. For hrtimers, new modes HRTIMER_ABS_PINNED and HRTIMER_REL_PINNED are added to queue cpu-pinned hrtimer. [ tglx: use .._PINNED mode argument instead of creating tons of new functions ] Signed-off-by: Arun R Bharadwaj <arun@linux.vnet.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * timers: allow deferrable timers for intervals tv2-tv5 to be deferredJon Hunter2009-05-021-0/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In the current kernel implementation only kernel timers for time interval tv1 are being deferred. This patch allows any timer that is configured as deferrable to be defer regardless of time interval. This patch was previously discussed in http://marc.info/?l=linux-kernel&m=123196343531966&w=2 and was acked by Venki Pallipadi, the author of the original deferrable timer patch. Signed-off-by: Jon Hunter <jon-hunter@ti.com> Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* | Merge branch 'linus' into x86/mce3Ingo Molnar2009-06-111-78/+11
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | Conflicts: arch/x86/kernel/cpu/mcheck/mce_64.c arch/x86/kernel/irq.c Merge reason: Resolve the conflicts above. Signed-off-by: Ingo Molnar <mingo@elte.hu>
| * \ Merge branch 'linus' into perfcounters/coreIngo Molnar2009-06-111-78/+8
| |\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Conflicts: arch/x86/kernel/irqinit.c arch/x86/kernel/irqinit_64.c arch/x86/kernel/traps.c arch/x86/mm/fault.c include/linux/sched.h kernel/exit.c
| | * | sched, timers: cleanup avenrun usersThomas Gleixner2009-05-151-26/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | avenrun is an rough estimate so we don't have to worry about consistency of the three avenrun values. Remove the xtime lock dependency and provide a function to scale the values. Cleanup the users. [ Impact: cleanup ] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org>
| | * | sched, timers: move calc_load() to schedulerThomas Gleixner2009-05-151-52/+2
| | |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Dimitri Sivanich noticed that xtime_lock is held write locked across calc_load() which iterates over all online CPUs. That can cause long latencies for xtime_lock readers on large SMP systems. The load average calculation is an rough estimate anyway so there is no real need to protect the readers vs. the update. It's not a problem when the avenrun array is updated while a reader copies the values. Instead of iterating over all online CPUs let the scheduler_tick code update the number of active tasks shortly before the avenrun update happens. The avenrun update itself is handled by the CPU which calls do_timer(). [ Impact: reduce xtime_lock write locked section ] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org>
| * | Merge branch 'linus' into perfcounters/coreIngo Molnar2009-04-291-2/+5
| |\ \ | | |/ | | | | | | | | | | | | | | | Merge reason: This brach was on -rc1, refresh it to almost-rc4 to pick up the latest upstream fixes. Signed-off-by: Ingo Molnar <mingo@elte.hu>
| * | perf_counter: unify and fix delayed counter wakeupPeter Zijlstra2009-04-061-0/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | While going over the wakeup code I noticed delayed wakeups only work for hardware counters but basically all software counters rely on them. This patch unifies and generalizes the delayed wakeup to fix this issue. Since we're dealing with NMI context bits here, use a cmpxchg() based single link list implementation to track counters that have pending wakeups. [ This should really be generic code for delayed wakeups, but since we cannot use cmpxchg()/xchg() in generic code, I've let it live in the perf_counter code. -- Eric Dumazet could use it to aggregate the network wakeups. ] Furthermore, the x86 method of using TIF flags was flawed in that its quite possible to end up setting the bit on the idle task, loosing the wakeup. The powerpc method uses per-cpu storage and does appear to be sufficient. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Paul Mackerras <paulus@samba.org> Orig-LKML-Reference: <20090330171023.153932974@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* | | Export add_timer_on for modulesAndi Kleen2009-05-281-0/+1
| |/ |/| | | | | | | | | | | | | | | Needed in followon patch. Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
* | Merge branches 'core-fixes-for-linus', 'irq-fixes-for-linus' and ↵Linus Torvalds2009-04-091-2/+5
|\ \ | |/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip * 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: printk: fix wrong format string iter for printk futex: comment requeue key reference semantics * 'irq-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: irq: fix cpumask memory leak on offstack cpumask kernels * 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: posix-timers: fix RLIMIT_CPU && setitimer(CPUCLOCK_PROF) posix-timers: fix RLIMIT_CPU && fork() timers: add missing kernel-doc
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