diff options
author | Ingo Molnar <mingo@elte.hu> | 2008-02-28 21:00:21 +0100 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2008-04-19 19:44:57 +0200 |
commit | 27ec4407790d075c325e1f4da0a19c56953cce23 (patch) | |
tree | d8c068c4743394eab173995bf085a99dfec257c7 /kernel | |
parent | 018d6db4cb5bbdcd65424a16f2dcca692ed32ae4 (diff) | |
download | linux-stable-27ec4407790d075c325e1f4da0a19c56953cce23.tar.gz linux-stable-27ec4407790d075c325e1f4da0a19c56953cce23.tar.bz2 linux-stable-27ec4407790d075c325e1f4da0a19c56953cce23.zip |
sched: make cpu_clock() globally synchronous
Alexey Zaytsev reported (and bisected) that the introduction of
cpu_clock() in printk made the timestamps jump back and forth.
Make cpu_clock() more reliable while still keeping it fast when it's
called frequently.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/sched.c | 52 |
1 files changed, 49 insertions, 3 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 8dcdec6fe0fe..7377222ab42f 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -632,11 +632,39 @@ int sysctl_sched_rt_runtime = 950000; */ #define RUNTIME_INF ((u64)~0ULL) +static const unsigned long long time_sync_thresh = 100000; + +static DEFINE_PER_CPU(unsigned long long, time_offset); +static DEFINE_PER_CPU(unsigned long long, prev_cpu_time); + /* - * For kernel-internal use: high-speed (but slightly incorrect) per-cpu - * clock constructed from sched_clock(): + * Global lock which we take every now and then to synchronize + * the CPUs time. This method is not warp-safe, but it's good + * enough to synchronize slowly diverging time sources and thus + * it's good enough for tracing: */ -unsigned long long cpu_clock(int cpu) +static DEFINE_SPINLOCK(time_sync_lock); +static unsigned long long prev_global_time; + +static unsigned long long __sync_cpu_clock(cycles_t time, int cpu) +{ + unsigned long flags; + + spin_lock_irqsave(&time_sync_lock, flags); + + if (time < prev_global_time) { + per_cpu(time_offset, cpu) += prev_global_time - time; + time = prev_global_time; + } else { + prev_global_time = time; + } + + spin_unlock_irqrestore(&time_sync_lock, flags); + + return time; +} + +static unsigned long long __cpu_clock(int cpu) { unsigned long long now; unsigned long flags; @@ -657,6 +685,24 @@ unsigned long long cpu_clock(int cpu) return now; } + +/* + * For kernel-internal use: high-speed (but slightly incorrect) per-cpu + * clock constructed from sched_clock(): + */ +unsigned long long cpu_clock(int cpu) +{ + unsigned long long prev_cpu_time, time, delta_time; + + prev_cpu_time = per_cpu(prev_cpu_time, cpu); + time = __cpu_clock(cpu) + per_cpu(time_offset, cpu); + delta_time = time-prev_cpu_time; + + if (unlikely(delta_time > time_sync_thresh)) + time = __sync_cpu_clock(time, cpu); + + return time; +} EXPORT_SYMBOL_GPL(cpu_clock); #ifndef prepare_arch_switch |