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Commit 81520183 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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perf: Optimize perf_swevent_ctx_event() 



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: <20091120212508.378188589@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 0cff784a

kernel/perf_event.c

+1 −6
Original line number Diff line number Diff line
@@ -3886,15 +3886,10 @@ static void perf_swevent_ctx_event(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_swevent_match(event, type, event_id, data, regs))

			perf_swevent_add(event, nr, nmi, data, regs);

	}

	rcu_read_unlock();

}



static int *perf_swevent_recursion_context(struct perf_cpu_context *cpuctx)
@@ -3926,9 +3921,9 @@ static void do_perf_sw_event(enum perf_type_id type, u32 event_id, 
	(*recursion)++;

	barrier();



	rcu_read_lock();

	perf_swevent_ctx_event(&cpuctx->ctx, type, event_id,

				 nr, nmi, data, regs);

	rcu_read_lock();

	/*

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

	 * events ends up in.