From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756230AbZBITEg (ORCPT ); Mon, 9 Feb 2009 14:04:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753289AbZBITE1 (ORCPT ); Mon, 9 Feb 2009 14:04:27 -0500 Received: from mx2.redhat.com ([66.187.237.31]:38292 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751784AbZBITE0 (ORCPT ); Mon, 9 Feb 2009 14:04:26 -0500 Date: Mon, 9 Feb 2009 17:04:06 -0200 From: Arnaldo Carvalho de Melo To: Steven Rostedt Cc: Ingo Molnar , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Linux Kernel Mailing List Subject: [PATCH tip 1/1] ring_buffer: pahole struct ring_buffer Message-ID: <20090209190406.GA11005@ghostprotocols.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Url: http://oops.ghostprotocols.net:81/blog User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, While fixing some bugs in pahole (built-in.o files were not being processed due to relocation problems) I found out about these packable structures: $ pahole --packable kernel/trace/ring_buffer.o | grep ring ring_buffer 72 64 8 ring_buffer_per_cpu 112 104 8 If we take a look at the current layout of struct ring_buffer we can see that we have two 4 bytes holes. $ pahole -C ring_buffer kernel/trace/ring_buffer.o struct ring_buffer { unsigned int pages; /* 0 4 */ unsigned int flags; /* 4 4 */ int cpus; /* 8 4 */ /* XXX 4 bytes hole, try to pack */ cpumask_var_t cpumask; /* 16 8 */ atomic_t record_disabled; /* 24 4 */ /* XXX 4 bytes hole, try to pack */ struct mutex mutex; /* 32 32 */ /* --- cacheline 1 boundary (64 bytes) --- */ struct ring_buffer_per_cpu * * buffers; /* 64 8 */ /* size: 72, cachelines: 2, members: 7 */ /* sum members: 64, holes: 2, sum holes: 8 */ /* last cacheline: 8 bytes */ }; So, if I ask pahole to reorganize it: $ pahole -C ring_buffer --reorganize kernel/trace/ring_buffer.o struct ring_buffer { unsigned int pages; /* 0 4 */ unsigned int flags; /* 4 4 */ int cpus; /* 8 4 */ atomic_t record_disabled; /* 12 4 */ cpumask_var_t cpumask; /* 16 8 */ struct mutex mutex; /* 24 32 */ struct ring_buffer_per_cpu * * buffers; /* 56 8 */ /* --- cacheline 1 boundary (64 bytes) --- */ /* size: 64, cachelines: 1, members: 7 */ }; /* saved 8 bytes and 1 cacheline! */ We get it using just one 64 bytes cacheline. To see what it did: $ pahole -C ring_buffer --reorganize --show_reorg_steps \ kernel/trace/ring_buffer.o | grep \/ /* Moving 'record_disabled' from after 'cpumask' to after 'cpus' */ Cc: Ingo Molnar Cc: Frédéric Weisbecker Signed-off-by: Arnaldo Carvalho de Melo --- ring_buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 53ba3a6..27ef3bf 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -273,8 +273,8 @@ struct ring_buffer { unsigned pages; unsigned flags; int cpus; - cpumask_var_t cpumask; atomic_t record_disabled; + cpumask_var_t cpumask; struct mutex mutex;