From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [RFC PATCH 2/3] sched: add yield_to function Date: Thu, 09 Dec 2010 23:34:46 -0500 Message-ID: <4D01ADE6.3010508@redhat.com> References: <20101202144129.4357fe00@annuminas.surriel.com> <20101202144423.3ad1908d@annuminas.surriel.com> <1291382619.32004.2124.camel@laptop> <20101203133056.GF27994@linux.vnet.ibm.com> <1291385010.32004.2165.camel@laptop> <20101203140607.GA9800@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Avi Kiviti , Ingo Molnar , Anthony Liguori To: vatsa@linux.vnet.ibm.com Return-path: In-Reply-To: <20101203140607.GA9800@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 12/03/2010 09:06 AM, Srivatsa Vaddagiri wrote: > On Fri, Dec 03, 2010 at 03:03:30PM +0100, Peter Zijlstra wrote: >> No, because they do receive service (they spend some time spinning >> before being interrupted), so the respective vruntimes will increase, at >> some point they'll pass B0 and it'll get scheduled. > > Is that sufficient to ensure that B0 receives its fair share (1/3 cpu in this > case)? I have a rough idea for a simpler way to ensure fairness. At yield_to time, we could track in the runqueue structure that a task received CPU time (and on the other runqueue that a task donated CPU time). The balancer can count time-given-to CPUs as busier, and donated-time CPUs as less busy, moving tasks away in the unlikely event that the same task gets keeping CPU time given to it. Conversely, it can move other tasks onto CPUs that have tasks on them that cannot make progress right now and are just donating their CPU time. Most of the time the time-given and time-received should balance out and there should be little to no influence on the load balancer. This code would just be there to deal with exceptional circumstances, to avoid the theoretical worst case people have described. -- All rights reversed