From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: question about VM kernel parameter idle= Date: Thu, 21 Nov 2013 09:22:00 +0200 Message-ID: <20131121072200.GE2108@redhat.com> References: <20131121070139.GL19005@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Zhanghaoyu (A)" , "qemu-devel@nongnu.org" , KVM , Paolo Bonzini , Luonengjun , "Huangweidong (C)" To: "Michael S. Tsirkin" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:28556 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750821Ab3KUHWo (ORCPT ); Thu, 21 Nov 2013 02:22:44 -0500 Content-Disposition: inline In-Reply-To: <20131121070139.GL19005@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, Nov 21, 2013 at 09:01:39AM +0200, Michael S. Tsirkin wrote: > On Thu, Nov 21, 2013 at 03:45:28AM +0000, Zhanghaoyu (A) wrote: > > Hi, all > > > > What's the difference of the linux guest kernel parameter idle=, especially in performance? > > > > Taking the performance into account, which one is best? > > > > In my opinion, if the number of all VMs' vcpus is far more than that of pcpus, e.g. SPECVirt test, idle=halt is better for server's total throughput, > > otherwise, e.g. in some CT scenario, the number of total vcpus is not greater than that of pcpus, idle=poll is better for server's total throughput, > > because of less latency and VMEXIT. > > Makes sense overall. > > > linux-3.9 and above, idle=mwait is not recommended. > > > > Thanks, > > Zhang Haoyu > > Does it actually have effect? I didn't think it would. mwait instruction is never exposed to a guest. With idle=mwait is will likely fall back to halt silently. -- Gleb.