From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function Date: Wed, 05 Jan 2011 11:08:06 +0200 Message-ID: <4D2434F6.4020904@redhat.com> References: <20110105110837.B62A.A69D9226@jp.fujitsu.com> <4D242D60.9060301@redhat.com> <20110105173823.B658.A69D9226@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Rik van Riel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Srivatsa Vaddagiri , Peter Zijlstra , Mike Galbraith , Chris Wright To: KOSAKI Motohiro Return-path: In-Reply-To: <20110105173823.B658.A69D9226@jp.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 01/05/2011 10:40 AM, KOSAKI Motohiro wrote: > > On 01/05/2011 04:39 AM, KOSAKI Motohiro wrote: > > > > On 01/04/2011 08:14 AM, KOSAKI Motohiro wrote: > > > > > Also, If pthread_cond_signal() call sys_yield_to imlicitly, we can > > > > > avoid almost Nehalem (and other P2P cache arch) lock unfairness > > > > > problem. (probaby creating pthread_condattr_setautoyield_np or similar > > > > > knob is good one) > > > > > > > > Often, the thread calling pthread_cond_signal() wants to continue > > > > executing, not yield. > > > > > > Then, it doesn't work. > > > > > > After calling pthread_cond_signal(), T1 which cond_signal caller and T2 > > > which waked start to GIL grab race. But usually T1 is always win because > > > lock variable is in T1's cpu cache. Why kernel and userland have so much > > > different result? One of a reason is glibc doesn't have any ticket lock scheme. > > > > > > If you are interesting GIL mess and issue, please feel free to ask more. > > > > I suggest looking into an explicit round-robin scheme, where each thread > > adds itself to a queue and an unlock wakes up the first waiter. > > I'm sure you haven't try your scheme. but I did. It's slow. Won't anything with a heavily contented global/giant lock be slow? What's the average lock hold time per thread? 10%? 50%? 90%? -- error compiling committee.c: too many arguments to function