Ingo Molnar wrote:So I pulled your tree and I would agree there was a problem. But it seems unrelated to kgdb. I bisected the tree because it worked starting with the kgdb-light merge. It fails once with the patch below, but it is not clear as to why other than the lock must have something to do with it. I'll submit a patch to the kgdb test suite to increase the amount of loops through the single step test as it is it can definitely catch things :-) Jason. From 84556fe84dd975161e70b782d7d7cc7bd080c06a Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mingo@elte.hu> Date: Thu, 28 Feb 2008 21:00:21 +0100 Subject: [PATCH 0883/1078] 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> --- kernel/sched.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++--- 1 files changed, 49 insertions(+), 3 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 8dcdec6..7377222 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 -- 1.5.5 --
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