From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751601AbaCPHaX (ORCPT ); Sun, 16 Mar 2014 03:30:23 -0400 Received: from mail-ee0-f43.google.com ([74.125.83.43]:49580 "EHLO mail-ee0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751075AbaCPHaW (ORCPT ); Sun, 16 Mar 2014 03:30:22 -0400 Message-ID: <1394955020.19079.3.camel@marge.simpson.net> Subject: Re: cond_resched() and RCU CPU stall warnings From: Mike Galbraith To: paulmck@linux.vnet.ibm.com Cc: peterz@infradead.org, mingo@elte.hu, josh@joshtriplett.org, laijs@cn.fujitsu.com, linux-kernel@vger.kernel.org Date: Sun, 16 Mar 2014 08:30:20 +0100 In-Reply-To: <20140316062501.GX21124@linux.vnet.ibm.com> References: <20140316015914.GA22102@linux.vnet.ibm.com> <1394950182.5470.15.camel@marge.simpson.net> <20140316062501.GX21124@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2014-03-15 at 23:25 -0700, Paul E. McKenney wrote: > On Sun, Mar 16, 2014 at 07:09:42AM +0100, Mike Galbraith wrote: > > Hm. Since you only care about the case where your task is solo, how > > about do racy checks, 100% accuracy isn't required is it? Seems you > > wouldn't want to unconditionally do that in tight loops. > > And indeed, my current workaround unconditionally does schedule() one > out of 256 loops. I would do something similar here, perhaps based > on per-CPU counters, perhaps even with racy accesses to avoid always > doing preempt_disable()/preempt_enable(). > > Or did you have something else in mind? Exactly what I meant, take a racy peek or two first. -Mike