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Commit d6ff86cf authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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perf: Optimize perf_event_task_ctx() 



Remove a rcu_read_{,un}lock() pair and a few conditionals.

We can remove the rcu_read_lock() by increasing the scope of one
in the calling function.

We can do away with the system_state check if the machine still
boots after this patch (seems to be the case).

We can do away with the list_empty() check because the bare
list_for_each_entry_rcu() reduces to that now that we've removed
everything else.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091120212508.452227115@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 81520183

kernel/perf_event.c

+1 −6
Original line number Diff line number Diff line
@@ -3267,15 +3267,10 @@ static void perf_event_task_ctx(struct perf_event_context *ctx, 
{

	struct perf_event *event;



	if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))

		return;



	rcu_read_lock();

	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {

		if (perf_event_task_match(event))

			perf_event_task_output(event, task_event);

	}

	rcu_read_unlock();

}



static void perf_event_task_event(struct perf_task_event *task_event)
@@ -3283,11 +3278,11 @@ static void perf_event_task_event(struct perf_task_event *task_event) 
	struct perf_cpu_context *cpuctx;

	struct perf_event_context *ctx = task_event->task_ctx;



	rcu_read_lock();

	cpuctx = &get_cpu_var(perf_cpu_context);

	perf_event_task_ctx(&cpuctx->ctx, task_event);

	put_cpu_var(perf_cpu_context);



	rcu_read_lock();

	if (!ctx)

		ctx = rcu_dereference(task_event->task->perf_event_ctxp);

	if (ctx)