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Commit a08b159f authored by Paul Mackerras's avatar Paul Mackerras Committed by Ingo Molnar
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perf_counter: don't count scheduler ticks as context switches 



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: default avatarPaul 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: default avatarIngo Molnar <mingo@elte.hu>
parent 6751b71e

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);