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Commit f6d9dd23 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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perf: Optimize perf_event_mmap_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: <20091120212508.606459548@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent f6595f3a

kernel/perf_event.c

+1 −6
Original line number Diff line number Diff line
@@ -3493,15 +3493,10 @@ static void perf_event_mmap_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_mmap_match(event, mmap_event))

			perf_event_mmap_output(event, mmap_event);

	}

	rcu_read_unlock();

}



static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
@@ -3557,11 +3552,11 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event) 


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



	rcu_read_lock();

	cpuctx = &get_cpu_var(perf_cpu_context);

	perf_event_mmap_ctx(&cpuctx->ctx, mmap_event);

	put_cpu_var(perf_cpu_context);



	rcu_read_lock();

	/*

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

	 * events ends up in.