From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751671Ab1ADRxu (ORCPT ); Tue, 4 Jan 2011 12:53:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:11763 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750997Ab1ADRxs (ORCPT ); Tue, 4 Jan 2011 12:53:48 -0500 Message-ID: <4D235E9D.1040603@redhat.com> Date: Tue, 04 Jan 2011 12:53:33 -0500 From: Rik van Riel 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.fc13 Lightning/1.0b3pre Thunderbird/3.1.7 MIME-Version: 1.0 To: Peter Zijlstra CC: Hillf Danton , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Avi Kiviti , Srivatsa Vaddagiri , Mike Galbraith , Chris Wright Subject: Re: [RFC -v3 PATCH 2/3] sched: add yield_to function References: <20110103162637.29f23c40@annuminas.surriel.com> <20110103162918.577a9620@annuminas.surriel.com> <4D234E60.3010804@redhat.com> <1294160890.2016.171.camel@laptop> In-Reply-To: <1294160890.2016.171.camel@laptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/04/2011 12:08 PM, Peter Zijlstra wrote: > On Wed, 2011-01-05 at 00:51 +0800, Hillf Danton wrote: >> Where is the yield_to callback in the patch for RT schedule class? >> If @p is RT, what could you do? > > RT guests are a pipe dream, you first need to get the hypervisor (kvm in > this case) to be RT, which it isn't. Then you either need to very > statically set-up the host and the guest scheduling constraints (not > possible with RR/FIFO) or have a complete paravirt RT scheduler which > communicates its requirements to the host. There's a limited use case. One host can have a few RT guests, say a host with 8 CPUs can have up to 6 or 7 RT VCPUs. Those guests get top priority. The host can then have some other, low priority, guests that scavenge remaining CPU time. In this case, no yield_to is required for RT guests, because they do not do overcommit. -- All rights reversed