perf_counter: don't count scheduler ticks as context switches (a08b159f) · Commits · 戴 / test

The context-switch software counter gives inflated values at present because each scheduler tick and each process-wide counter enable/disable prctl gets counted as a context switch. This happens because perf_counter_task_tick, perf_counter_task_disable and perf_counter_task_enable all call perf_counter_task_sched_out, which calls perf_swcounter_event to record a context switch event. This fixes it by introducing a variant of perf_counter_task_sched_out with two underscores in front for internal use within the perf_counter code, and makes perf_counter_task_{tick,disable,enable} call it. This variant doesn't record a context switch event, and takes a struct perf_counter_context *. This adds the new variant rather than changing the behaviour or interface of perf_counter_task_sched_out because that is called from other code. [ Impact: fix inflated context-switch event counts ] Signed-off-by:

Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com> LKML-Reference: <18951.48034.485580.498953@drongo.ozlabs.ibm.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/perf_counter.c

+11 −5

Original line number	Diff line number	Diff line
		@@ -837,6 +837,14 @@ void perf_counter_task_sched_out(struct task_struct *task, int cpu)
		cpuctx->task_ctx = NULL;
		}

		static void __perf_counter_task_sched_out(struct perf_counter_context *ctx)
		{
		struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);

		__perf_counter_sched_out(ctx, cpuctx);
		cpuctx->task_ctx = NULL;
		}

		static void perf_counter_cpu_sched_out(struct perf_cpu_context *cpuctx)
		{
		__perf_counter_sched_out(&cpuctx->ctx, cpuctx);
		@@ -943,15 +951,13 @@ int perf_counter_task_disable(void)
		struct perf_counter *counter;
		unsigned long flags;
		u64 perf_flags;
		int cpu;

		if (likely(!ctx->nr_counters))
		return 0;

		local_irq_save(flags);
		cpu = smp_processor_id();

		perf_counter_task_sched_out(curr, cpu);
		__perf_counter_task_sched_out(ctx);

		spin_lock(&ctx->lock);

		@@ -989,7 +995,7 @@ int perf_counter_task_enable(void)
		local_irq_save(flags);
		cpu = smp_processor_id();

		perf_counter_task_sched_out(curr, cpu);
		__perf_counter_task_sched_out(ctx);

		spin_lock(&ctx->lock);

		@@ -1054,7 +1060,7 @@ void perf_counter_task_tick(struct task_struct *curr, int cpu)
		ctx = &curr->perf_counter_ctx;

		perf_counter_cpu_sched_out(cpuctx);
		perf_counter_task_sched_out(curr, cpu);
		__perf_counter_task_sched_out(ctx);

		rotate_ctx(&cpuctx->ctx);
		rotate_ctx(ctx);

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