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perf_counter: don't count scheduler ticks as context switches

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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>
This commit is contained in:
Paul Mackerras 2009-05-11 15:46:10 +10:00 committed by Ingo Molnar
parent 6751b71ea2
commit a08b159fc2
1 changed files with 11 additions and 5 deletions
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16
kernel/perf_counter.c
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@ -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);