From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 1/3 v2] wait: introduce wait_event_exclusive_cmd Date: Wed, 29 Apr 2015 11:31:09 +0200 Message-ID: <20150429093109.GS5029@twins.programming.kicks-ass.net> References: <1430275735-20290-1-git-send-email-yuanhan.liu@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1430275735-20290-1-git-send-email-yuanhan.liu@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Yuanhan Liu Cc: neilb@suse.de, linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar List-Id: linux-raid.ids On Wed, Apr 29, 2015 at 10:48:53AM +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_exclusive_cmd 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 Thanks! Assuming you want to route this through Neil's MD tree: Acked-by: Peter Zijlstra (Intel) > --- > include/linux/wait.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/include/linux/wait.h b/include/linux/wait.h > index 2db8334..db78c72 100644 > --- a/include/linux/wait.h > +++ b/include/linux/wait.h > @@ -358,6 +358,19 @@ do { \ > __ret; \ > }) > > +#define __wait_event_exclusive_cmd(wq, condition, cmd1, cmd2) \ > + (void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, 1, 0, \ > + cmd1; schedule(); cmd2) > +/* > + * Just like wait_event_cmd(), except it sets exclusive flag > + */ > +#define wait_event_exclusive_cmd(wq, condition, cmd1, cmd2) \ > +do { \ > + if (condition) \ > + break; \ > + __wait_event_exclusive_cmd(wq, condition, cmd1, cmd2); \ > +} while (0) > + > #define __wait_event_cmd(wq, condition, cmd1, cmd2) \ > (void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, 0, \ > cmd1; schedule(); cmd2) > -- > 1.9.0 >