perf: Optimize perf_event_mmap_ctx() (f6d9dd23) · Commits · 戴 / test

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:

Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> LKML-Reference: <20091120212508.606459548@chello.nl> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

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 @@ got_name:

		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.

Admin message