Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030739AbbD1ON3 (ORCPT ); Tue, 28 Apr 2015 10:13:29 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:51635 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030376AbbD1ON2 (ORCPT ); Tue, 28 Apr 2015 10:13:28 -0400 Date: Tue, 28 Apr 2015 16:13:15 +0200 From: Peter Zijlstra To: Yuanhan Liu Cc: neilb@suse.de, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: [PATCH 1/3] wait: introduce wait_event_cmd_exclusive Message-ID: <20150428141315.GD23123@twins.programming.kicks-ass.net> References: <1430110263-23977-1-git-send-email-yuanhan.liu@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1430110263-23977-1-git-send-email-yuanhan.liu@linux.intel.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2224 Lines: 60 On Mon, Apr 27, 2015 at 12:51:01PM +0800, Yuanhan Liu wrote: > It's just a variant of wait_event_cmd, with exclusive flag being set. > > For cases like RAID5, which puts many processes to sleep until 1/4 > resources are free, a wake_up wakes up all processes to run, but > there is one process being able to get the resource as it's protected > by a spin lock. That ends up introducing heavy lock contentions, and > hurts performance badly. > > Here introduce wait_event_cmd_exclusive to relieve the lock contention > naturally by letting wake_up() just wake up one process. > > Cc: Ingo Molnar > Cc: Peter Zijlstra > Signed-off-by: Yuanhan Liu > --- > include/linux/wait.h | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/include/linux/wait.h b/include/linux/wait.h > index 2db8334..6c3b4de 100644 > --- a/include/linux/wait.h > +++ b/include/linux/wait.h > @@ -358,10 +358,18 @@ do { \ > __ret; \ > }) > > -#define __wait_event_cmd(wq, condition, cmd1, cmd2) \ > - (void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, 0, \ > +#define __wait_event_cmd(wq, condition, cmd1, cmd2, exclusive) \ > + (void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, exclusive, 0, \ > cmd1; schedule(); cmd2) > > + > +#define wait_event_cmd_exclusive(wq, condition, cmd1, cmd2) \ > +do { \ > + if (condition) \ > + break; \ > + __wait_event_cmd(wq, condition, cmd1, cmd2, 1); \ > +} while (0) > + > /** > * wait_event_cmd - sleep until a condition gets true > * @wq: the waitqueue to wait on > @@ -380,7 +388,7 @@ do { \ > do { \ > if (condition) \ > break; \ > - __wait_event_cmd(wq, condition, cmd1, cmd2); \ > + __wait_event_cmd(wq, condition, cmd1, cmd2, 0); \ > } while (0) > No, that's wrong, its assumed that wait*() and __wait*() have the same arguments. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/