diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/Changes | 43 | ||||
| -rw-r--r-- | Documentation/CodingStyle | 4 | ||||
| -rw-r--r-- | Documentation/arm/kernel_user_helpers.txt | 267 | ||||
| -rw-r--r-- | Documentation/cgroups/blkio-controller.txt | 12 | ||||
| -rw-r--r-- | Documentation/feature-removal-schedule.txt | 22 | ||||
| -rw-r--r-- | Documentation/filesystems/caching/netfs-api.txt | 16 | ||||
| -rw-r--r-- | Documentation/hwmon/f71882fg | 4 | ||||
| -rw-r--r-- | Documentation/hwmon/k10temp | 8 | ||||
| -rw-r--r-- | Documentation/kernel-parameters.txt | 2 | ||||
| -rw-r--r-- | Documentation/laptops/thinkpad-acpi.txt | 5 | ||||
| -rw-r--r-- | Documentation/power/runtime_pm.txt | 26 | ||||
| -rw-r--r-- | Documentation/spinlocks.txt | 45 |
12 files changed, 376 insertions, 78 deletions
diff --git a/Documentation/Changes b/Documentation/Changes index 5f4828a034e3..b17580885273 100644 --- a/Documentation/Changes +++ b/Documentation/Changes @@ -2,13 +2,7 @@ Intro ===== This document is designed to provide a list of the minimum levels of -software necessary to run the 2.6 kernels, as well as provide brief -instructions regarding any other "Gotchas" users may encounter when -trying life on the Bleeding Edge. If upgrading from a pre-2.4.x -kernel, please consult the Changes file included with 2.4.x kernels for -additional information; most of that information will not be repeated -here. Basically, this document assumes that your system is already -functional and running at least 2.4.x kernels. +software necessary to run the 3.0 kernels. This document is originally based on my "Changes" file for 2.0.x kernels and therefore owes credit to the same people as that file (Jared Mauch, @@ -22,11 +16,10 @@ Upgrade to at *least* these software revisions before thinking you've encountered a bug! If you're unsure what version you're currently running, the suggested command should tell you. -Again, keep in mind that this list assumes you are already -functionally running a Linux 2.4 kernel. Also, not all tools are -necessary on all systems; obviously, if you don't have any ISDN -hardware, for example, you probably needn't concern yourself with -isdn4k-utils. +Again, keep in mind that this list assumes you are already functionally +running a Linux kernel. Also, not all tools are necessary on all +systems; obviously, if you don't have any ISDN hardware, for example, +you probably needn't concern yourself with isdn4k-utils. o Gnu C 3.2 # gcc --version o Gnu make 3.80 # make --version @@ -114,12 +107,12 @@ Ksymoops If the unthinkable happens and your kernel oopses, you may need the ksymoops tool to decode it, but in most cases you don't. -In the 2.6 kernel it is generally preferred to build the kernel with -CONFIG_KALLSYMS so that it produces readable dumps that can be used as-is -(this also produces better output than ksymoops). -If for some reason your kernel is not build with CONFIG_KALLSYMS and -you have no way to rebuild and reproduce the Oops with that option, then -you can still decode that Oops with ksymoops. +It is generally preferred to build the kernel with CONFIG_KALLSYMS so +that it produces readable dumps that can be used as-is (this also +produces better output than ksymoops). If for some reason your kernel +is not build with CONFIG_KALLSYMS and you have no way to rebuild and +reproduce the Oops with that option, then you can still decode that Oops +with ksymoops. Module-Init-Tools ----------------- @@ -261,8 +254,8 @@ needs to be recompiled or (preferably) upgraded. NFS-utils --------- -In 2.4 and earlier kernels, the nfs server needed to know about any -client that expected to be able to access files via NFS. This +In ancient (2.4 and earlier) kernels, the nfs server needed to know +about any client that expected to be able to access files via NFS. This information would be given to the kernel by "mountd" when the client mounted the filesystem, or by "exportfs" at system startup. exportfs would take information about active clients from /var/lib/nfs/rmtab. @@ -272,11 +265,11 @@ which is not always easy, particularly when trying to implement fail-over. Even when the system is working well, rmtab suffers from getting lots of old entries that never get removed. -With 2.6 we have the option of having the kernel tell mountd when it -gets a request from an unknown host, and mountd can give appropriate -export information to the kernel. This removes the dependency on -rmtab and means that the kernel only needs to know about currently -active clients. +With modern kernels we have the option of having the kernel tell mountd +when it gets a request from an unknown host, and mountd can give +appropriate export information to the kernel. This removes the +dependency on rmtab and means that the kernel only needs to know about +currently active clients. To enable this new functionality, you need to: diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 58b0bf917834..fa6e25b94a54 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -680,8 +680,8 @@ ones already enabled by DEBUG. Chapter 14: Allocating memory The kernel provides the following general purpose memory allocators: -kmalloc(), kzalloc(), kcalloc(), and vmalloc(). Please refer to the API -documentation for further information about them. +kmalloc(), kzalloc(), kcalloc(), vmalloc(), and vzalloc(). Please refer to +the API documentation for further information about them. The preferred form for passing a size of a struct is the following: diff --git a/Documentation/arm/kernel_user_helpers.txt b/Documentation/arm/kernel_user_helpers.txt new file mode 100644 index 000000000000..a17df9f91d16 --- /dev/null +++ b/Documentation/arm/kernel_user_helpers.txt @@ -0,0 +1,267 @@ +Kernel-provided User Helpers +============================ + +These are segment of kernel provided user code reachable from user space +at a fixed address in kernel memory. This is used to provide user space +with some operations which require kernel help because of unimplemented +native feature and/or instructions in many ARM CPUs. The idea is for this +code to be executed directly in user mode for best efficiency but which is +too intimate with the kernel counter part to be left to user libraries. +In fact this code might even differ from one CPU to another depending on +the available instruction set, or whether it is a SMP systems. In other +words, the kernel reserves the right to change this code as needed without +warning. Only the entry points and their results as documented here are +guaranteed to be stable. + +This is different from (but doesn't preclude) a full blown VDSO +implementation, however a VDSO would prevent some assembly tricks with +constants that allows for efficient branching to those code segments. And +since those code segments only use a few cycles before returning to user +code, the overhead of a VDSO indirect far call would add a measurable +overhead to such minimalistic operations. + +User space is expected to bypass those helpers and implement those things +inline (either in the code emitted directly by the compiler, or part of +the implementation of a library call) when optimizing for a recent enough +processor that has the necessary native support, but only if resulting +binaries are already to be incompatible with earlier ARM processors due to +useage of similar native instructions for other things. In other words +don't make binaries unable to run on earlier processors just for the sake +of not using these kernel helpers if your compiled code is not going to +use new instructions for other purpose. + +New helpers may be added over time, so an older kernel may be missing some +helpers present in a newer kernel. For this reason, programs must check +the value of __kuser_helper_version (see below) before assuming that it is +safe to call any particular helper. This check should ideally be +performed only once at process startup time, and execution aborted early +if the required helpers are not provided by the kernel version that +process is running on. + +kuser_helper_version +-------------------- + +Location: 0xffff0ffc + +Reference declaration: + + extern int32_t __kuser_helper_version; + +Definition: + + This field contains the number of helpers being implemented by the + running kernel. User space may read this to determine the availability + of a particular helper. + +Usage example: + +#define __kuser_helper_version (*(int32_t *)0xffff0ffc) + +void check_kuser_version(void) +{ + if (__kuser_helper_version < 2) { + fprintf(stderr, "can't do atomic operations, kernel too old\n"); + abort(); + } +} + +Notes: + + User space may assume that the value of this field never changes + during the lifetime of any single process. This means that this + field can be read once during the initialisation of a library or + startup phase of a program. + +kuser_get_tls +------------- + +Location: 0xffff0fe0 + +Reference prototype: + + void * __kuser_get_tls(void); + +Input: + + lr = return address + +Output: + + r0 = TLS value + +Clobbered registers: + + none + +Definition: + + Get the TLS value as previously set via the __ARM_NR_set_tls syscall. + +Usage example: + +typedef void * (__kuser_get_tls_t)(void); +#define __kuser_get_tls (*(__kuser_get_tls_t *)0xffff0fe0) + +void foo() +{ + void *tls = __kuser_get_tls(); + printf("TLS = %p\n", tls); +} + +Notes: + + - Valid only if __kuser_helper_version >= 1 (from kernel version 2.6.12). + +kuser_cmpxchg +------------- + +Location: 0xffff0fc0 + +Reference prototype: + + int __kuser_cmpxchg(int32_t oldval, int32_t newval, volatile int32_t *ptr); + +Input: + + r0 = oldval + r1 = newval + r2 = ptr + lr = return address + +Output: + + r0 = success code (zero or non-zero) + C flag = set if r0 == 0, clear if r0 != 0 + +Clobbered registers: + + r3, ip, flags + +Definition: + + Atomically store newval in *ptr only if *ptr is equal to oldval. + Return zero if *ptr was changed or non-zero if no exchange happened. + The C flag is also set if *ptr was changed to allow for assembly + optimization in the calling code. + +Usage example: + +typedef int (__kuser_cmpxchg_t)(int oldval, int newval, volatile int *ptr); +#define __kuser_cmpxchg (*(__kuser_cmpxchg_t *)0xffff0fc0) + +int atomic_add(volatile int *ptr, int val) +{ + int old, new; + + do { + old = *ptr; + new = old + val; + } while(__kuser_cmpxchg(old, new, ptr)); + + return new; +} + +Notes: + + - This routine already includes memory barriers as needed. + + - Valid only if __kuser_helper_version >= 2 (from kernel version 2.6.12). + +kuser_memory_barrier +-------------------- + +Location: 0xffff0fa0 + +Reference prototype: + + void __kuser_memory_barrier(void); + +Input: + + lr = return address + +Output: + + none + +Clobbered registers: + + none + +Definition: + + Apply any needed memory barrier to preserve consistency with data modified + manually and __kuser_cmpxchg usage. + +Usage example: + +typedef void (__kuser_dmb_t)(void); +#define __kuser_dmb (*(__kuser_dmb_t *)0xffff0fa0) + +Notes: + + - Valid only if __kuser_helper_version >= 3 (from kernel version 2.6.15). + +kuser_cmpxchg64 +--------------- + +Location: 0xffff0f60 + +Reference prototype: + + int __kuser_cmpxchg64(const int64_t *oldval, + const int64_t *newval, + volatile int64_t *ptr); + +Input: + + r0 = pointer to oldval + r1 = pointer to newval + r2 = pointer to target value + lr = return address + +Output: + + r0 = success code (zero or non-zero) + C flag = set if r0 == 0, clear if r0 != 0 + +Clobbered registers: + + r3, lr, flags + +Definition: + + Atomically store the 64-bit value pointed by *newval in *ptr only if *ptr + is equal to the 64-bit value pointed by *oldval. Return zero if *ptr was + changed or non-zero if no exchange happened. + + The C flag is also set if *ptr was changed to allow for assembly + optimization in the calling code. + +Usage example: + +typedef int (__kuser_cmpxchg64_t)(const int64_t *oldval, + const int64_t *newval, + volatile int64_t *ptr); +#define __kuser_cmpxchg64 (*(__kuser_cmpxchg64_t *)0xffff0f60) + +int64_t atomic_add64(volatile int64_t *ptr, int64_t val) +{ + int64_t old, new; + + do { + old = *ptr; + new = old + val; + } while(__kuser_cmpxchg64(&old, &new, ptr)); + + return new; +} + +Notes: + + - This routine already includes memory barriers as needed. + + - Due to the length of this sequence, this spans 2 conventional kuser + "slots", therefore 0xffff0f80 is not used as a valid entry point. + + - Valid only if __kuser_helper_version >= 5 (from kernel version 3.1). diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt index cd45c8ea7463..84f0a15fc210 100644 --- a/Documentation/cgroups/blkio-controller.txt +++ b/Documentation/cgroups/blkio-controller.txt @@ -77,7 +77,7 @@ Throttling/Upper Limit policy - Specify a bandwidth rate on particular device for root group. The format for policy is "<major>:<minor> <byes_per_second>". - echo "8:16 1048576" > /sys/fs/cgroup/blkio/blkio.read_bps_device + echo "8:16 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device Above will put a limit of 1MB/second on reads happening for root group on device having major/minor number 8:16. @@ -90,7 +90,7 @@ Throttling/Upper Limit policy 1024+0 records out 4194304 bytes (4.2 MB) copied, 4.0001 s, 1.0 MB/s - Limits for writes can be put using blkio.write_bps_device file. + Limits for writes can be put using blkio.throttle.write_bps_device file. Hierarchical Cgroups ==================== @@ -286,28 +286,28 @@ Throttling/Upper limit policy files specified in bytes per second. Rules are per deivce. Following is the format. - echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.read_bps_device + echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.throttle.read_bps_device - blkio.throttle.write_bps_device - Specifies upper limit on WRITE rate to the device. IO rate is specified in bytes per second. Rules are per deivce. Following is the format. - echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.write_bps_device + echo "<major>:<minor> <rate_bytes_per_second>" > /cgrp/blkio.throttle.write_bps_device - blkio.throttle.read_iops_device - Specifies upper limit on READ rate from the device. IO rate is specified in IO per second. Rules are per deivce. Following is the format. - echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.read_iops_device + echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.throttle.read_iops_device - blkio.throttle.write_iops_device - Specifies upper limit on WRITE rate to the device. IO rate is specified in io per second. Rules are per deivce. Following is the format. - echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.write_iops_device + echo "<major>:<minor> <rate_io_per_second>" > /cgrp/blkio.throttle.write_iops_device Note: If both BW and IOPS rules are specified for a device, then IO is subjectd to both the constraints. diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt index 72e238465b0b..b1c921c27519 100644 --- a/Documentation/feature-removal-schedule.txt +++ b/Documentation/feature-removal-schedule.txt @@ -583,3 +583,25 @@ Why: Superseded by the UVCIOC_CTRL_QUERY ioctl. Who: Laurent Pinchart <laurent.pinchart@ideasonboard.com> ---------------------------- + +What: For VIDIOC_S_FREQUENCY the type field must match the device node's type. + If not, return -EINVAL. +When: 3.2 +Why: It makes no sense to switch the tuner to radio mode by calling + VIDIOC_S_FREQUENCY on a video node, or to switch the tuner to tv mode by + calling VIDIOC_S_FREQUENCY on a radio node. This is the first step of a + move to more consistent handling of tv and radio tuners. +Who: Hans Verkuil <hans.verkuil@cisco.com> + +---------------------------- + +What: Opening a radio device node will no longer automatically switch the + tuner mode from tv to radio. +When: 3.3 +Why: Just opening a V4L device should not change the state of the hardware + like that. It's very unexpected and against the V4L spec. Instead, you + switch to radio mode by calling VIDIOC_S_FREQUENCY. This is the second + and last step of the move to consistent handling of tv and radio tuners. +Who: Hans Verkuil <hans.verkuil@cisco.com> + +---------------------------- diff --git a/Documentation/filesystems/caching/netfs-api.txt b/Documentation/filesystems/caching/netfs-api.txt index a167ab876c35..7cc6bf2871eb 100644 --- a/Documentation/filesystems/caching/netfs-api.txt +++ b/Documentation/filesystems/caching/netfs-api.txt @@ -673,6 +673,22 @@ storage request to complete, or it may attempt to cancel the storage request - in which case the page will not be stored in the cache this time. +BULK INODE PAGE UNCACHE +----------------------- + +A convenience routine is provided to perform an uncache on all the pages +attached to an inode. This assumes that the pages on the inode correspond on a +1:1 basis with the pages in the cache. + + void fscache_uncache_all_inode_pages(struct fscache_cookie *cookie, + struct inode *inode); + +This takes the netfs cookie that the pages were cached with and the inode that +the pages are attached to. This function will wait for pages to finish being +written to the cache and for the cache to finish with the page generally. No +error is returned. + + ========================== INDEX AND DATA FILE UPDATE ========================== diff --git a/Documentation/hwmon/f71882fg b/Documentation/hwmon/f71882fg index 84d2623810f3..de91c0db5846 100644 --- a/Documentation/hwmon/f71882fg +++ b/Documentation/hwmon/f71882fg @@ -22,6 +22,10 @@ Supported chips: Prefix: 'f71869' Addresses scanned: none, address read from Super I/O config space Datasheet: Available from the Fintek website + * Fintek F71869A + Prefix: 'f71869a' + Addresses scanned: none, address read from Super I/O config space + Datasheet: Not public * Fintek F71882FG and F71883FG Prefix: 'f71882fg' Addresses scanned: none, address read from Super I/O config space diff --git a/Documentation/hwmon/k10temp b/Documentation/hwmon/k10temp index 0393c89277c0..a10f73624ad3 100644 --- a/Documentation/hwmon/k10temp +++ b/Documentation/hwmon/k10temp @@ -9,8 +9,8 @@ Supported chips: Socket S1G3: Athlon II, Sempron, Turion II * AMD Family 11h processors: Socket S1G2: Athlon (X2), Sempron (X2), Turion X2 (Ultra) -* AMD Family 12h processors: "Llano" -* AMD Family 14h processors: "Brazos" (C/E/G-Series) +* AMD Family 12h processors: "Llano" (E2/A4/A6/A8-Series) +* AMD Family 14h processors: "Brazos" (C/E/G/Z-Series) * AMD Family 15h processors: "Bulldozer" Prefix: 'k10temp' @@ -20,12 +20,16 @@ Supported chips: http://support.amd.com/us/Processor_TechDocs/31116.pdf BIOS and Kernel Developer's Guide (BKDG) for AMD Family 11h Processors: http://support.amd.com/us/Processor_TechDocs/41256.pdf + BIOS and Kernel Developer's Guide (BKDG) for AMD Family 12h Processors: + http://support.amd.com/us/Processor_TechDocs/41131.pdf BIOS and Kernel Developer's Guide (BKDG) for AMD Family 14h Models 00h-0Fh Processors: http://support.amd.com/us/Processor_TechDocs/43170.pdf Revision Guide for AMD Family 10h Processors: http://support.amd.com/us/Processor_TechDocs/41322.pdf Revision Guide for AMD Family 11h Processors: http://support.amd.com/us/Processor_TechDocs/41788.pdf + Revision Guide for AMD Family 12h Processors: + http://support.amd.com/us/Processor_TechDocs/44739.pdf Revision Guide for AMD Family 14h Models 00h-0Fh Processors: http://support.amd.com/us/Processor_TechDocs/47534.pdf AMD Family 11h Processor Power and Thermal Data Sheet for Notebooks: diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index fd248a318211..aa47be71df4c 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2015,6 +2015,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. the default. off: Turn ECRC off on: Turn ECRC on. + realloc reallocate PCI resources if allocations done by BIOS + are erroneous. pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power Management. diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt index 1565eefd6fd5..61815483efa3 100644 --- a/Documentation/laptops/thinkpad-acpi.txt +++ b/Documentation/laptops/thinkpad-acpi.txt @@ -534,6 +534,8 @@ Events that are never propagated by the driver: 0x2404 System is waking up from hibernation to undock 0x2405 System is waking up from hibernation to eject bay 0x5010 Brightness level changed/control event +0x6000 KEYBOARD: Numlock key pressed +0x6005 KEYBOARD: Fn key pressed (TO BE VERIFIED) Events that are propagated by the driver to userspace: @@ -545,6 +547,8 @@ Events that are propagated by the driver to userspace: 0x3006 Bay hotplug request (hint to power up SATA link when the optical drive tray is ejected) 0x4003 Undocked (see 0x2x04), can sleep again +0x4010 Docked into hotplug port replicator (non-ACPI dock) +0x4011 Undocked from hotplug port replicator (non-ACPI dock) 0x500B Tablet pen inserted into its storage bay 0x500C Tablet pen removed from its storage bay 0x6011 ALARM: battery is too hot @@ -552,6 +556,7 @@ Events that are propagated by the driver to userspace: 0x6021 ALARM: a sensor is too hot 0x6022 ALARM: a sensor is extremely hot 0x6030 System thermal table changed +0x6040 Nvidia Optimus/AC adapter related (TO BE VERIFIED) Battery nearly empty alarms are a last resort attempt to get the operating system to hibernate or shutdown cleanly (0x2313), or shutdown diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt index 22accb3eb40e..b24875b1ced5 100644 --- a/Documentation/power/runtime_pm.txt +++ b/Documentation/power/runtime_pm.txt @@ -501,13 +501,29 @@ helper functions described in Section 4. In that case, pm_runtime_resume() should be used. Of course, for this purpose the device's run-time PM has to be enabled earlier by calling pm_runtime_enable(). -If the device bus type's or driver's ->probe() or ->remove() callback runs +If the device bus type's or driver's ->probe() callback runs pm_runtime_suspend() or pm_runtime_idle() or their asynchronous counterparts, they will fail returning -EAGAIN, because the device's usage counter is -incremented by the core before executing ->probe() and ->remove(). Still, it -may be desirable to suspend the device as soon as ->probe() or ->remove() has -finished, so the PM core uses pm_runtime_idle_sync() to invoke the -subsystem-level idle callback for the device at that time. +incremented by the driver core before executing ->probe(). Still, it may be +desirable to suspend the device as soon as ->probe() has finished, so the driver +core uses pm_runtime_put_sync() to invoke the subsystem-level idle callback for +the device at that time. + +Moreover, the driver core prevents runtime PM callbacks from racing with the bus +notifier callback in __device_release_driver(), which is necessary, because the +notifier is used by some subsystems to carry out operations affecting the +runtime PM functionality. It does so by calling pm_runtime_get_sync() before +driver_sysfs_remove() and the BUS_NOTIFY_UNBIND_DRIVER notifications. This +resumes the device if it's in the suspended state and prevents it from +being suspended again while those routines are being executed. + +To allow bus types and drivers to put devices into the suspended state by +calling pm_runtime_suspend() from their ->remove() routines, the driver core +executes pm_runtime_put_sync() after running the BUS_NOTIFY_UNBIND_DRIVER +notifications in __device_release_driver(). This requires bus types and +drivers to make their ->remove() callbacks avoid races with runtime PM directly, +but also it allows of more flexibility in the handling of devices during the +removal of their drivers. The user space can effectively disallow the driver of the device to power manage it at run time by changing the value of its /sys/devices/.../power/control diff --git a/Documentation/spinlocks.txt b/Documentation/spinlocks.txt index 2e3c64b1a6a5..9dbe885ecd8d 100644 --- a/Documentation/spinlocks.txt +++ b/Documentation/spinlocks.txt @@ -13,18 +13,8 @@ static DEFINE_SPINLOCK(xxx_lock); The above is always safe. It will disable interrupts _locally_, but the spinlock itself will guarantee the global lock, so it will guarantee that there is only one thread-of-control within the region(s) protected by that -lock. This works well even under UP. The above sequence under UP -essentially is just the same as doing - - unsigned long flags; - - save_flags(flags); cli(); - ... critical section ... - restore_flags(flags); - -so the code does _not_ need to worry about UP vs SMP issues: the spinlocks -work correctly under both (and spinlocks are actually more efficient on -architectures that allow doing the "save_flags + cli" in one operation). +lock. This works well even under UP also, so the code does _not_ need to +worry about UP vs SMP issues: the spinlocks work correctly under both. NOTE! Implications of spin_locks for memory are further described in: @@ -36,27 +26,7 @@ The above is usually pretty simple (you usually need and want only one spinlock for most things - using more than one spinlock can make things a lot more complex and even slower and is usually worth it only for sequences that you _know_ need to be split up: avoid it at all cost if you -aren't sure). HOWEVER, it _does_ mean that if you have some code that does - - cli(); - .. critical section .. - sti(); - -and another sequence that does - - spin_lock_irqsave(flags); - .. critical section .. - spin_unlock_irqrestore(flags); - -then they are NOT mutually exclusive, and the critical regions can happen -at the same time on two different CPU's. That's fine per se, but the -critical regions had better be critical for different things (ie they -can't stomp on each other). - -The above is a problem mainly if you end up mixing code - for example the -routines in ll_rw_block() tend to use cli/sti to protect the atomicity of -their actions, and if a driver uses spinlocks instead then you should -think about issues like the above. +aren't sure). This is really the only really hard part about spinlocks: once you start using spinlocks they tend to expand to areas you might not have noticed @@ -120,11 +90,10 @@ Lesson 3: spinlocks revisited. The single spin-lock primitives above are by no means the only ones. They are the most safe ones, and the ones that work under all circumstances, -but partly _because_ they are safe they are also fairly slow. They are -much faster than a generic global cli/sti pair, but slower than they'd -need to be, because they do have to disable interrupts (which is just a -single instruction on a x86, but it's an expensive one - and on other -architectures it can be worse). +but partly _because_ they are safe they are also fairly slow. They are slower +than they'd need to be, because they do have to disable interrupts +(which is just a single instruction on a x86, but it's an expensive one - +and on other architectures it can be worse). If you have a case where you have to protect a data structure across several CPU's and you want to use spinlocks you can potentially use |
