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author | Thomas Gleixner <tglx@linutronix.de> | 2007-10-11 11:17:24 +0200 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2007-10-11 11:17:24 +0200 |
commit | 250c22777fe1ccd7ac588579a6c16db4c0161cc5 (patch) | |
tree | 55c317efb7d792ec6fdae1d1937c67a502c48dec /arch/x86/kernel/tsc_sync.c | |
parent | x86_64: move ia32 (diff) | |
download | linux-250c22777fe1ccd7ac588579a6c16db4c0161cc5.tar.xz linux-250c22777fe1ccd7ac588579a6c16db4c0161cc5.zip |
x86_64: move kernel
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/kernel/tsc_sync.c')
-rw-r--r-- | arch/x86/kernel/tsc_sync.c | 188 |
1 files changed, 187 insertions, 1 deletions
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 12424629af87..355f5f506c81 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -1 +1,187 @@ -#include "../../x86_64/kernel/tsc_sync.c" +/* + * 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 + tsc_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("check_tsc_sync_source failed"); + 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 + |