From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Wright Subject: Re: [PATCH] qemu-kvm: introduce cpu_start/cpu_stop commands Date: Mon, 22 Nov 2010 15:56:51 -0800 Message-ID: <20101122235651.GD10050@sequoia.sous-sol.org> References: <1290466818-5230-1-git-send-email-aliguori@us.ibm.com> <20101122230405.GB10050@sequoia.sous-sol.org> <4CEB006C.8010407@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Chris Wright , Anthony Liguori , qemu-devel@nongnu.org, kvm@vger.kernel.org To: Anthony Liguori Return-path: Received: from sous-sol.org ([216.99.217.87]:54044 "EHLO sequoia.sous-sol.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932393Ab0KVX5G (ORCPT ); Mon, 22 Nov 2010 18:57:06 -0500 Content-Disposition: inline In-Reply-To: <4CEB006C.8010407@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: * Anthony Liguori (aliguori@linux.vnet.ibm.com) wrote: > On 11/22/2010 05:04 PM, Chris Wright wrote: > >* Anthony Liguori (aliguori@us.ibm.com) wrote: > >>qemu-kvm vcpu threads don't response to SIGSTOP/SIGCONT. Instead of teaching > >>them to respond to these signals, introduce monitor commands that stop and start > >>individual vcpus. > >In the past SIGSTOP has introduced time skew. Have you verified this > >isn't an issue. > > Time skew is a big topic. Are you talking about TSC drift, > pit/rtc/hpet drift, etc? Sorry to be vague, but it's been long enough that I don't recall the details. The guest kernel's clocksource effected how timekeeping progressed across STOP/CONT (was probably missing qemu based timer ticks). While this is not the same, made me wonder if you'd tested against that. > It's certainly going to stress periodic interrupt catch up code. Heh, call it a feature for autotest ;) thanks, -chris From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=46355 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PKgFu-0002cL-3P for qemu-devel@nongnu.org; Mon, 22 Nov 2010 18:57:06 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PKgFs-000294-Vj for qemu-devel@nongnu.org; Mon, 22 Nov 2010 18:57:05 -0500 Received: from sous-sol.org ([216.99.217.87]:43838 helo=sequoia.sous-sol.org) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PKgFs-00028v-I9 for qemu-devel@nongnu.org; Mon, 22 Nov 2010 18:57:04 -0500 Date: Mon, 22 Nov 2010 15:56:51 -0800 From: Chris Wright Message-ID: <20101122235651.GD10050@sequoia.sous-sol.org> References: <1290466818-5230-1-git-send-email-aliguori@us.ibm.com> <20101122230405.GB10050@sequoia.sous-sol.org> <4CEB006C.8010407@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4CEB006C.8010407@linux.vnet.ibm.com> Subject: [Qemu-devel] Re: [PATCH] qemu-kvm: introduce cpu_start/cpu_stop commands List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Chris Wright , Anthony Liguori , qemu-devel@nongnu.org, kvm@vger.kernel.org * Anthony Liguori (aliguori@linux.vnet.ibm.com) wrote: > On 11/22/2010 05:04 PM, Chris Wright wrote: > >* Anthony Liguori (aliguori@us.ibm.com) wrote: > >>qemu-kvm vcpu threads don't response to SIGSTOP/SIGCONT. Instead of teaching > >>them to respond to these signals, introduce monitor commands that stop and start > >>individual vcpus. > >In the past SIGSTOP has introduced time skew. Have you verified this > >isn't an issue. > > Time skew is a big topic. Are you talking about TSC drift, > pit/rtc/hpet drift, etc? Sorry to be vague, but it's been long enough that I don't recall the details. The guest kernel's clocksource effected how timekeeping progressed across STOP/CONT (was probably missing qemu based timer ticks). While this is not the same, made me wonder if you'd tested against that. > It's certainly going to stress periodic interrupt catch up code. Heh, call it a feature for autotest ;) thanks, -chris