From a08b159fc243dbfe415250466d24cfc5010deee5 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Mon, 11 May 2009 15:46:10 +1000 Subject: [PATCH] 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: Paul Mackerras Cc: Peter Zijlstra Cc: Corey Ashford LKML-Reference: <18951.48034.485580.498953@drongo.ozlabs.ibm.com> Signed-off-by: Ingo Molnar --- kernel/perf_counter.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index a5bdc93..7373b96 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -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); -- 2.7.4