linux-kernel - [tip:perf/core] perf: Optimize perf_event_mmap

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Message-ID: <tip-f6d9dd237da400effb265f3554c64413f8a3e7b4@git.kernel.org>
Date:	Sat, 21 Nov 2009 13:42:10 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:perf/core] perf: Optimize perf_event_mmap_ctx()

Commit-ID:  f6d9dd237da400effb265f3554c64413f8a3e7b4
Gitweb:     http://git.kernel.org/tip/f6d9dd237da400effb265f3554c64413f8a3e7b4
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Fri, 20 Nov 2009 22:19:48 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sat, 21 Nov 2009 14:11:37 +0100

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: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul Mackerras <paulus@...ba.org>
LKML-Reference: <20091120212508.606459548@...llo.nl>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/perf_event.c |    7 +------
 1 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 4deefaa..68fbf4f 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -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.
--
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