From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC -v3 PATCH 0/3] directed yield for Pause Loop Exiting Date: Tue, 04 Jan 2011 12:35:15 +0200 Message-ID: <4D22F7E3.7000508@redhat.com> References: <20110103162637.29f23c40@annuminas.surriel.com> <1294123335.11283.26.camel@marge.simson.net> <4D22E3C0.7010808@redhat.com> <1294137134.4379.9.camel@marge.simson.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Rik van Riel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Srivatsa Vaddagiri , Peter Zijlstra , Chris Wright To: Mike Galbraith Return-path: In-Reply-To: <1294137134.4379.9.camel@marge.simson.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 01/04/2011 12:32 PM, Mike Galbraith wrote: > On Tue, 2011-01-04 at 11:09 +0200, Avi Kivity wrote: > > On 01/04/2011 08:42 AM, Mike Galbraith wrote: > > > > If I were to, say, run a 256 CPU VM on my quad, would this help me get > > > more hackbench or whatever oomph from my (256X80386/20:) box? > > > > First of all, you can't run 256 guests on x86 kvm. > > I didn't want 256 guests. Just one great big dog slow virtual playpen :) I meant a 256 vcpu guest. Certainly you can run 256 guests, you're limited only by virtual memory. Current kvm limit is 64 vcpus. > > > > Both Intel and AMD CPUs have a feature that detects when a virtual > > > > CPU is spinning on a lock and will trap to the host. > > > > > > Does an Intel Q6600 have this trap gizmo (iow will this do anything at > > > all for my little box if I were to try it out). > > > > Likely not. Run > > http://git.kernel.org/?p=virt/kvm/qemu-kvm.git;a=blob_plain;f=kvm/scripts/vmxcap;hb=HEAD, > > look for 'PAUSE-loop exiting'. I think the first processors to include > > them were the Nehalem-EXs, and Westmeres have them as well. > > Oh darn, need new box to get all the toys. Thanks. > I have a patchset somewhere that emulates pause-loop exiting by looking at rip during timer interrupts. Unfortunately timer interrupts are very rare compared to pause-loop exits, so it's not very helpful. -- error compiling committee.c: too many arguments to function