From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751235AbVHTVZE (ORCPT ); Sat, 20 Aug 2005 17:25:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751237AbVHTVZD (ORCPT ); Sat, 20 Aug 2005 17:25:03 -0400 Received: from highlandsun.propagation.net ([66.221.212.168]:17934 "EHLO highlandsun.propagation.net") by vger.kernel.org with ESMTP id S1751235AbVHTVZB (ORCPT ); Sat, 20 Aug 2005 17:25:01 -0400 Message-ID: <43079FA9.700@symas.com> Date: Sat, 20 Aug 2005 14:24:57 -0700 From: Howard Chu User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8b4) Gecko/20050810 SeaMonkey/1.0a MIME-Version: 1.0 To: Lee Revell CC: Nick Piggin , Robert Hancock , linux-kernel Subject: Re: sched_yield() makes OpenLDAP slow References: <4D8eT-4rg-31@gated-at.bofh.it> <4306A176.3090907@shaw.ca> <4306AF26.3030106@yahoo.com.au> <4307788E.1040209@symas.com> <1124571437.2115.3.camel@mindpipe> In-Reply-To: <1124571437.2115.3.camel@mindpipe> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Lee Revell wrote: > On Sat, 2005-08-20 at 11:38 -0700, Howard Chu wrote: > > But I also found that I needed to add a new yield(), to work around > > yet another unexpected issue on this system - we have a number of > > threads waiting on a condition variable, and the thread holding the > > mutex signals the var, unlocks the mutex, and then immediately > > relocks it. The expectation here is that upon unlocking the mutex, > > the calling thread would block while some waiting thread (that just > > got signaled) would get to run. In fact what happened is that the > > calling thread unlocked and relocked the mutex without allowing any > > of the waiting threads to run. In this case the only solution was > > to insert a yield() after the mutex_unlock(). > > That's exactly the behavior I would expect. Why would you expect > unlocking a mutex to cause a reschedule, if the calling thread still > has timeslice left? That's beside the point. Folks are making an assertion that sched_yield() is meaningless; this example demonstrates that there are cases where sched_yield() is essential. -- -- Howard Chu Chief Architect, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc OpenLDAP Core Team http://www.openldap.org/project/