From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [patch 4/8] KVM: x86: replace hrtimer based timer emulation Date: Wed, 08 Jul 2009 19:36:42 +0300 Message-ID: <4A54CB1A.7090900@redhat.com> References: <20090706015511.923596553@localhost.localdomain> <20090706015812.786509491@localhost.localdomain> <4A54A202.9080602@redhat.com> <20090708162404.GA6803@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from mx2.redhat.com ([66.187.237.31]:56511 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753834AbZGHQeM (ORCPT ); Wed, 8 Jul 2009 12:34:12 -0400 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id n68GYC1R030445 for ; Wed, 8 Jul 2009 12:34:12 -0400 In-Reply-To: <20090708162404.GA6803@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 07/08/2009 07:24 PM, Marcelo Tosatti wrote: >> I wonder if we're really winning with this. Guests should be >> scheduled-out-but-not-halted rarely, and in all other cases we need to >> keep the timer. A timer comparison on each guest entry might be >> expensive (maybe not so much with tsc based timers). >> > > Any activity outside of guest mode that takes more than the period of > the timer (think 1000Hz) causes unnecessary host load. > > Booting a RHEL5 UP without VNC or serial output on an idle host: > > timer_int_normal=95416 timer_interrupt_accumulated=873 > > (and it continues to increase in that rate, roughly 1%). > > Now factor in multiple guests, loaded host, and you'll probably see more > than that. > If you're using qcow, you may be seeing the non-aio accesses. Otherwise, I can't think what can cause 1ms latency. Random host process? long mmu resync? -- error compiling committee.c: too many arguments to function