perf_counter: minimize context time updates (bce379bf) · Commits · 戴 / test

Push the update_context_time() calls up the stack so that we get less invokations and thereby a less noisy output: before: # ./perfstat -e 1:0 -e 1:1 -e 1:1 -e 1:1 -l ls > /dev/null Performance counter stats for 'ls': 10.163691 cpu clock ticks (msecs) (scaled from 98.94%) 10.215360 task clock ticks (msecs) (scaled from 98.18%) 10.185549 task clock ticks (msecs) (scaled from 98.53%) 10.183581 task clock ticks (msecs) (scaled from 98.71%) Wall-clock time elapsed: 11.912858 msecs after: # ./perfstat -e 1:0 -e 1:1 -e 1:1 -e 1:1 -l ls > /dev/null Performance counter stats for 'ls': 9.316630 cpu clock ticks (msecs) 9.280789 task clock ticks (msecs) 9.280789 task clock ticks (msecs) 9.280789 task clock ticks (msecs) Wall-clock time elapsed: 9.574872 msecs Signed-off-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com> LKML-Reference: <20090406094518.618876874@chello.nl> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/perf_counter.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -319,6 +319,8 @@ static void __perf_counter_disable(void *info)

		spin_lock_irqsave(&ctx->lock, flags);

		update_context_time(ctx);

		/*
		* If the counter is on, turn it off.
		* If it is in error state, leave it in error state.
		@@ -797,6 +799,8 @@ void perf_counter_task_sched_out(struct task_struct *task, int cpu)
		if (likely(!cpuctx->task_ctx))
		return;

		update_context_time(ctx);

		regs = task_pt_regs(task);
		perf_swcounter_event(PERF_COUNT_CONTEXT_SWITCHES, 1, 1, regs);
		__perf_counter_sched_out(ctx, cpuctx);
		@@ -2336,7 +2340,6 @@ static void task_clock_perf_counter_update(struct perf_counter *counter)
		u64 prev, now;
		s64 delta;

		update_context_time(counter->ctx);
		now = counter->ctx->time;

		prev = atomic64_xchg(&counter->hw.prev_count, now);
		@@ -2349,7 +2352,6 @@ static int task_clock_perf_counter_enable(struct perf_counter *counter)
		struct hw_perf_counter *hwc = &counter->hw;
		u64 now;

		update_context_time(counter->ctx);
		now = counter->ctx->time;

		atomic64_set(&hwc->prev_count, now);
		@@ -2372,6 +2374,7 @@ static void task_clock_perf_counter_disable(struct perf_counter *counter)

		static void task_clock_perf_counter_read(struct perf_counter *counter)
		{
		update_context_time(counter->ctx);
		task_clock_perf_counter_update(counter);
		}

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