Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760848Ab3EALCf (ORCPT ); Wed, 1 May 2013 07:02:35 -0400 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:35175 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756263Ab3EALC1 (ORCPT ); Wed, 1 May 2013 07:02:27 -0400 Date: Wed, 1 May 2013 13:00:47 +0200 From: Peter Zijlstra To: kosaki.motohiro@gmail.com Cc: linux-kernel@vger.kernel.org, Olivier Langlois , Martin Schwidefsky , Steven Rostedt , David Miller , Thomas Gleixner , Frederic Weisbecker , Ingo Molnar , KOSAKI Motohiro Subject: Re: [PATCH 09/10] sched: task_sched_runtime introduce micro optimization Message-ID: <20130501110047.GD28253@dyad.programming.kicks-ass.net> References: <1367291838-5490-1-git-send-email-kosaki.motohiro@gmail.com> <1367291838-5490-10-git-send-email-kosaki.motohiro@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1367291838-5490-10-git-send-email-kosaki.motohiro@gmail.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1409 Lines: 44 On Mon, Apr 29, 2013 at 11:17:17PM -0400, kosaki.motohiro@gmail.com wrote: > From: KOSAKI Motohiro > > rq lock in task_sched_runtime() is necessary for two reasons. 1) > accessing se.sum_exec_runtime is inatomic on 32bit and 2) > do_task_delta_exec() require it. > > And then, 64bit can avoid holds rq lock when add_delta is false. > > Signed-off-by: KOSAKI Motohiro > --- > kernel/sched/core.c | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b817e6d..24ba1c6 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2657,6 +2657,12 @@ unsigned long long task_sched_runtime(struct task_struct *p, bool add_delta) > struct rq *rq; > u64 ns = 0; > > + /* Micro optimization. */ Instead of the above; how about something like: /* 64-bit doesn't need locks to atomically read a 64bit value */ > +#ifdef CONFIG_64BIT > + if (!add_delta) > + return p->se.sum_exec_runtime; > +#endif > + > rq = task_rq_lock(p, &flags); > ns = p->se.sum_exec_runtime; > if (add_delta) > -- > 1.7.1 > -- 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/