diff options
Diffstat (limited to 'arch/x86_64/kernel')
| -rw-r--r-- | arch/x86_64/kernel/Makefile | 2 | ||||
| -rw-r--r-- | arch/x86_64/kernel/smpboot.c | 230 | ||||
| -rw-r--r-- | arch/x86_64/kernel/time.c | 11 | ||||
| -rw-r--r-- | arch/x86_64/kernel/tsc_sync.c | 187 |
4 files changed, 210 insertions, 220 deletions
diff --git a/arch/x86_64/kernel/Makefile b/arch/x86_64/kernel/Makefile index ae399458024b..6465eee6d920 100644 --- a/arch/x86_64/kernel/Makefile +++ b/arch/x86_64/kernel/Makefile @@ -19,7 +19,7 @@ obj-$(CONFIG_ACPI) += acpi/ obj-$(CONFIG_X86_MSR) += msr.o obj-$(CONFIG_MICROCODE) += microcode.o obj-$(CONFIG_X86_CPUID) += cpuid.o -obj-$(CONFIG_SMP) += smp.o smpboot.o trampoline.o +obj-$(CONFIG_SMP) += smp.o smpboot.o trampoline.o tsc_sync.o obj-y += apic.o nmi.o obj-y += io_apic.o mpparse.o \ genapic.o genapic_cluster.o genapic_flat.o diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c index daf19332f0dd..62d828433c30 100644 --- a/arch/x86_64/kernel/smpboot.c +++ b/arch/x86_64/kernel/smpboot.c @@ -148,217 +148,6 @@ static void __cpuinit smp_store_cpu_info(int id) print_cpu_info(c); } -/* - * New Funky TSC sync algorithm borrowed from IA64. - * Main advantage is that it doesn't reset the TSCs fully and - * in general looks more robust and it works better than my earlier - * attempts. I believe it was written by David Mosberger. Some minor - * adjustments for x86-64 by me -AK - * - * Original comment reproduced below. - * - * Synchronize TSC of the current (slave) CPU with the TSC of the - * MASTER CPU (normally the time-keeper CPU). We use a closed loop to - * eliminate the possibility of unaccounted-for errors (such as - * getting a machine check in the middle of a calibration step). The - * basic idea is for the slave to ask the master what itc value it has - * and to read its own itc before and after the master responds. Each - * iteration gives us three timestamps: - * - * slave master - * - * t0 ---\ - * ---\ - * ---> - * tm - * /--- - * /--- - * t1 <--- - * - * - * The goal is to adjust the slave's TSC such that tm falls exactly - * half-way between t0 and t1. If we achieve this, the clocks are - * synchronized provided the interconnect between the slave and the - * master is symmetric. Even if the interconnect were asymmetric, we - * would still know that the synchronization error is smaller than the - * roundtrip latency (t0 - t1). - * - * When the interconnect is quiet and symmetric, this lets us - * synchronize the TSC to within one or two cycles. However, we can - * only *guarantee* that the synchronization is accurate to within a - * round-trip time, which is typically in the range of several hundred - * cycles (e.g., ~500 cycles). In practice, this means that the TSCs - * are usually almost perfectly synchronized, but we shouldn't assume - * that the accuracy is much better than half a micro second or so. - * - * [there are other errors like the latency of RDTSC and of the - * WRMSR. These can also account to hundreds of cycles. So it's - * probably worse. It claims 153 cycles error on a dual Opteron, - * but I suspect the numbers are actually somewhat worse -AK] - */ - -#define MASTER 0 -#define SLAVE (SMP_CACHE_BYTES/8) - -/* Intentionally don't use cpu_relax() while TSC synchronization - because we don't want to go into funky power save modi or cause - hypervisors to schedule us away. Going to sleep would likely affect - latency and low latency is the primary objective here. -AK */ -#define no_cpu_relax() barrier() - -static __cpuinitdata DEFINE_SPINLOCK(tsc_sync_lock); -static volatile __cpuinitdata unsigned long go[SLAVE + 1]; -static int notscsync __cpuinitdata; - -#undef DEBUG_TSC_SYNC - -#define NUM_ROUNDS 64 /* magic value */ -#define NUM_ITERS 5 /* likewise */ - -/* Callback on boot CPU */ -static __cpuinit void sync_master(void *arg) -{ - unsigned long flags, i; - - go[MASTER] = 0; - - local_irq_save(flags); - { - for (i = 0; i < NUM_ROUNDS*NUM_ITERS; ++i) { - while (!go[MASTER]) - no_cpu_relax(); - go[MASTER] = 0; - rdtscll(go[SLAVE]); - } - } - local_irq_restore(flags); -} - -/* - * Return the number of cycles by which our tsc differs from the tsc - * on the master (time-keeper) CPU. A positive number indicates our - * tsc is ahead of the master, negative that it is behind. - */ -static inline long -get_delta(long *rt, long *master) -{ - unsigned long best_t0 = 0, best_t1 = ~0UL, best_tm = 0; - unsigned long tcenter, t0, t1, tm; - int i; - - for (i = 0; i < NUM_ITERS; ++i) { - rdtscll(t0); - go[MASTER] = 1; - while (!(tm = go[SLAVE])) - no_cpu_relax(); - go[SLAVE] = 0; - rdtscll(t1); - - if (t1 - t0 < best_t1 - best_t0) - best_t0 = t0, best_t1 = t1, best_tm = tm; - } - - *rt = best_t1 - best_t0; - *master = best_tm - best_t0; - - /* average best_t0 and best_t1 without overflow: */ - tcenter = (best_t0/2 + best_t1/2); - if (best_t0 % 2 + best_t1 % 2 == 2) - ++tcenter; - return tcenter - best_tm; -} - -static __cpuinit void sync_tsc(unsigned int master) -{ - int i, done = 0; - long delta, adj, adjust_latency = 0; - unsigned long flags, rt, master_time_stamp, bound; -#ifdef DEBUG_TSC_SYNC - static struct syncdebug { - long rt; /* roundtrip time */ - long master; /* master's timestamp */ - long diff; /* difference between midpoint and master's timestamp */ - long lat; /* estimate of tsc adjustment latency */ - } t[NUM_ROUNDS] __cpuinitdata; -#endif - - printk(KERN_INFO "CPU %d: Syncing TSC to CPU %u.\n", - smp_processor_id(), master); - - go[MASTER] = 1; - - /* It is dangerous to broadcast IPI as cpus are coming up, - * as they may not be ready to accept them. So since - * we only need to send the ipi to the boot cpu direct - * the message, and avoid the race. - */ - smp_call_function_single(master, sync_master, NULL, 1, 0); - - while (go[MASTER]) /* wait for master to be ready */ - no_cpu_relax(); - - spin_lock_irqsave(&tsc_sync_lock, flags); - { - for (i = 0; i < NUM_ROUNDS; ++i) { - delta = get_delta(&rt, &master_time_stamp); - if (delta == 0) { - done = 1; /* let's lock on to this... */ - bound = rt; - } - - if (!done) { - unsigned long t; - if (i > 0) { - adjust_latency += -delta; - adj = -delta + adjust_latency/4; - } else - adj = -delta; - - rdtscll(t); - wrmsrl(MSR_IA32_TSC, t + adj); - } -#ifdef DEBUG_TSC_SYNC - t[i].rt = rt; - t[i].master = master_time_stamp; - t[i].diff = delta; - t[i].lat = adjust_latency/4; -#endif - } - } - spin_unlock_irqrestore(&tsc_sync_lock, flags); - -#ifdef DEBUG_TSC_SYNC - for (i = 0; i < NUM_ROUNDS; ++i) - printk("rt=%5ld master=%5ld diff=%5ld adjlat=%5ld\n", - t[i].rt, t[i].master, t[i].diff, t[i].lat); -#endif - - printk(KERN_INFO - "CPU %d: synchronized TSC with CPU %u (last diff %ld cycles, " - "maxerr %lu cycles)\n", - smp_processor_id(), master, delta, rt); -} - -static void __cpuinit tsc_sync_wait(void) -{ - /* - * When the CPU has synchronized TSCs assume the BIOS - * or the hardware already synced. Otherwise we could - * mess up a possible perfect synchronization with a - * not-quite-perfect algorithm. - */ - if (notscsync || !cpu_has_tsc || !unsynchronized_tsc()) - return; - sync_tsc(0); -} - -static __init int notscsync_setup(char *s) -{ - notscsync = 1; - return 1; -} -__setup("notscsync", notscsync_setup); - static atomic_t init_deasserted __cpuinitdata; /* @@ -546,6 +335,11 @@ void __cpuinit start_secondary(void) /* otherwise gcc will move up the smp_processor_id before the cpu_init */ barrier(); + /* + * Check TSC sync first: + */ + check_tsc_sync_target(); + Dprintk("cpu %d: setting up apic clock\n", smp_processor_id()); setup_secondary_APIC_clock(); @@ -565,14 +359,6 @@ void __cpuinit start_secondary(void) */ set_cpu_sibling_map(smp_processor_id()); - /* - * Wait for TSC sync to not schedule things before. - * We still process interrupts, which could see an inconsistent - * time in that window unfortunately. - * Do this here because TSC sync has global unprotected state. - */ - tsc_sync_wait(); - /* * We need to hold call_lock, so there is no inconsistency * between the time smp_call_function() determines number of @@ -592,6 +378,7 @@ void __cpuinit start_secondary(void) cpu_set(smp_processor_id(), cpu_online_map); per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE; spin_unlock(&vector_lock); + unlock_ipi_call_lock(); cpu_idle(); @@ -1168,6 +955,11 @@ int __cpuinit __cpu_up(unsigned int cpu) /* Unleash the CPU! */ Dprintk("waiting for cpu %d\n", cpu); + /* + * Make sure and check TSC sync: + */ + check_tsc_sync_source(cpu); + while (!cpu_isset(cpu, cpu_online_map)) cpu_relax(); diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c index 3cc6886f1fb7..8cb2b2d35f5d 100644 --- a/arch/x86_64/kernel/time.c +++ b/arch/x86_64/kernel/time.c @@ -944,12 +944,23 @@ void __init time_init(void) #endif } +static int tsc_unstable = 0; + +void mark_tsc_unstable(void) +{ + tsc_unstable = 1; +} +EXPORT_SYMBOL_GPL(mark_tsc_unstable); + /* * Make an educated guess if the TSC is trustworthy and synchronized * over all CPUs. */ __cpuinit int unsynchronized_tsc(void) { + if (tsc_unstable) + return 1; + #ifdef CONFIG_SMP if (apic_is_clustered_box()) return 1; diff --git a/arch/x86_64/kernel/tsc_sync.c b/arch/x86_64/kernel/tsc_sync.c new file mode 100644 index 000000000000..014f0db45dfa --- /dev/null +++ b/arch/x86_64/kernel/tsc_sync.c @@ -0,0 +1,187 @@ +/* + * arch/x86_64/kernel/tsc_sync.c: check TSC synchronization. + * + * Copyright (C) 2006, Red Hat, Inc., Ingo Molnar + * + * We check whether all boot CPUs have their TSC's synchronized, + * print a warning if not and turn off the TSC clock-source. + * + * The warp-check is point-to-point between two CPUs, the CPU + * initiating the bootup is the 'source CPU', the freshly booting + * CPU is the 'target CPU'. + * + * Only two CPUs may participate - they can enter in any order. + * ( The serial nature of the boot logic and the CPU hotplug lock + * protects against more than 2 CPUs entering this code. ) + */ +#include <linux/spinlock.h> +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/smp.h> +#include <linux/nmi.h> +#include <asm/tsc.h> + +/* + * Entry/exit counters that make sure that both CPUs + * run the measurement code at once: + */ +static __cpuinitdata atomic_t start_count; +static __cpuinitdata atomic_t stop_count; + +/* + * We use a raw spinlock in this exceptional case, because + * we want to have the fastest, inlined, non-debug version + * of a critical section, to be able to prove TSC time-warps: + */ +static __cpuinitdata raw_spinlock_t sync_lock = __RAW_SPIN_LOCK_UNLOCKED; +static __cpuinitdata cycles_t last_tsc; +static __cpuinitdata cycles_t max_warp; +static __cpuinitdata int nr_warps; + +/* + * TSC-warp measurement loop running on both CPUs: + */ +static __cpuinit void check_tsc_warp(void) +{ + cycles_t start, now, prev, end; + int i; + + start = get_cycles_sync(); + /* + * The measurement runs for 20 msecs: + */ + end = start + cpu_khz * 20ULL; + now = start; + + for (i = 0; ; i++) { + /* + * We take the global lock, measure TSC, save the + * previous TSC that was measured (possibly on + * another CPU) and update the previous TSC timestamp. + */ + __raw_spin_lock(&sync_lock); + prev = last_tsc; + now = get_cycles_sync(); + last_tsc = now; + __raw_spin_unlock(&sync_lock); + + /* + * Be nice every now and then (and also check whether + * measurement is done [we also insert a 100 million + * loops safety exit, so we dont lock up in case the + * TSC readout is totally broken]): + */ + if (unlikely(!(i & 7))) { + if (now > end || i > 100000000) + break; + cpu_relax(); + touch_nmi_watchdog(); + } + /* + * Outside the critical section we can now see whether + * we saw a time-warp of the TSC going backwards: + */ + if (unlikely(prev > now)) { + __raw_spin_lock(&sync_lock); + max_warp = max(max_warp, prev - now); + nr_warps++; + __raw_spin_unlock(&sync_lock); + } + + } +} + +/* + * Source CPU calls into this - it waits for the freshly booted + * target CPU to arrive and then starts the measurement: + */ +void __cpuinit check_tsc_sync_source(int cpu) +{ + int cpus = 2; + + /* + * No need to check if we already know that the TSC is not + * synchronized: + */ + if (unsynchronized_tsc()) + return; + + printk(KERN_INFO "checking TSC synchronization [CPU#%d -> CPU#%d]:", + smp_processor_id(), cpu); + + /* + * Reset it - in case this is a second bootup: + */ + atomic_set(&stop_count, 0); + + /* + * Wait for the target to arrive: + */ + while (atomic_read(&start_count) != cpus-1) + cpu_relax(); + /* + * Trigger the target to continue into the measurement too: + */ + atomic_inc(&start_count); + + check_tsc_warp(); + + while (atomic_read(&stop_count) != cpus-1) + cpu_relax(); + + /* + * Reset it - just in case we boot another CPU later: + */ + atomic_set(&start_count, 0); + + if (nr_warps) { + printk("\n"); + printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs," + " turning off TSC clock.\n", max_warp); + mark_tsc_unstable(); + nr_warps = 0; + max_warp = 0; + last_tsc = 0; + } else { + printk(" passed.\n"); + } + + /* + * Let the target continue with the bootup: + */ + atomic_inc(&stop_count); +} + +/* + * Freshly booted CPUs call into this: + */ +void __cpuinit check_tsc_sync_target(void) +{ + int cpus = 2; + + if (unsynchronized_tsc()) + return; + + /* + * Register this CPU's participation and wait for the + * source CPU to start the measurement: + */ + atomic_inc(&start_count); + while (atomic_read(&start_count) != cpus) + cpu_relax(); + + check_tsc_warp(); + + /* + * Ok, we are done: + */ + atomic_inc(&stop_count); + + /* + * Wait for the source CPU to print stuff: + */ + while (atomic_read(&stop_count) != cpus) + cpu_relax(); +} +#undef NR_LOOPS + |
