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Commit f6595f3a authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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perf: Optimize perf_event_comm_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: <20091120212508.527608793@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent d6ff86cf

kernel/perf_event.c

+1 −6
Original line number Diff line number Diff line
@@ -3374,15 +3374,10 @@ static void perf_event_comm_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_comm_match(event))

			perf_event_comm_output(event, comm_event);

	}

	rcu_read_unlock();

}



static void perf_event_comm_event(struct perf_comm_event *comm_event)
@@ -3401,11 +3396,11 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event) 


	comm_event->event_id.header.size = sizeof(comm_event->event_id) + size;



	rcu_read_lock();

	cpuctx = &get_cpu_var(perf_cpu_context);

	perf_event_comm_ctx(&cpuctx->ctx, comm_event);

	put_cpu_var(perf_cpu_context);



	rcu_read_lock();

	/*

	 * doesn't really matter which of the child contexts the

	 * events ends up in.