Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755234Ab0LQPJx (ORCPT ); Fri, 17 Dec 2010 10:09:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:15723 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755149Ab0LQPJw (ORCPT ); Fri, 17 Dec 2010 10:09:52 -0500 Message-ID: <4D0B7D24.5060207@redhat.com> Date: Fri, 17 Dec 2010 17:09:24 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.13) Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Thunderbird/3.1.7 MIME-Version: 1.0 To: Mike Galbraith CC: Rik van Riel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Srivatsa Vaddagiri , Peter Zijlstra , Chris Wright Subject: Re: [RFC -v2 PATCH 2/3] sched: add yield_to function References: <20101213224434.7495edb2@annuminas.surriel.com> <20101213224657.7e141746@annuminas.surriel.com> <1292306896.7448.157.camel@marge.simson.net> <4D0A6D34.6070806@redhat.com> <1292569018.7772.75.camel@marge.simson.net> In-Reply-To: <1292569018.7772.75.camel@marge.simson.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1378 Lines: 32 On 12/17/2010 08:56 AM, Mike Galbraith wrote: > > Surely that makes it a reasonable idea to call yield, and > > get one of the other tasks on the current CPU running for > > a bit? > > There's nothing wrong with trying to give up the cpu. It's the concept > of a cross cpu yield_to() that I find mighty strange. What's so strange about it? From a high level there are N runnable tasks contending for M cpus. If task X really needs task Y to run, what does it matter if task Y last ran on the same cpu as task X or not? Do I correctly read between the lines that CFS maintains complete fairness only on a cpu, but not globally? I hope I'm wrong, but PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ P COMMAND 8648 avi 20 0 106m 1092 148 R 80.4 0.0 0:26.03 1 bash 8656 avi 20 0 106m 1080 136 R 47.3 0.0 0:14.73 0 bash 8652 avi 20 0 106m 1080 136 R 47.0 0.0 0:15.36 0 bash doesn't look too good (three infinite loops in bash started at the roughly same time) -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- 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/