From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH 1/2] kvm tools: Respect ISR status in virtio header Date: Sat, 07 May 2011 10:01:39 -0500 Message-ID: <4DC55ED3.1080006@us.ibm.com> References: <1304735660-10844-1-git-send-email-asias.hejun@gmail.com> <20110507093027.GD27657@elte.hu> <4DC545BA.3030501@us.ibm.com> <1304779834.10621.14.camel@jaguar> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ingo Molnar , Asias He , "Michael S. Tsirkin" , Rusty Russell , Mark McLoughlin , Cyrill Gorcunov , Sasha Levin , Prasad Joshi , kvm@vger.kernel.org To: Pekka Enberg Return-path: Received: from e38.co.us.ibm.com ([32.97.110.159]:58432 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755448Ab1EGPBq (ORCPT ); Sat, 7 May 2011 11:01:46 -0400 Received: from d03relay05.boulder.ibm.com (d03relay05.boulder.ibm.com [9.17.195.107]) by e38.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id p477SUgs017801 for ; Sat, 7 May 2011 01:28:30 -0600 Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by d03relay05.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p47F1fGJ308534 for ; Sat, 7 May 2011 09:01:41 -0600 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p47F6hVK007810 for ; Sat, 7 May 2011 09:06:44 -0600 In-Reply-To: <1304779834.10621.14.camel@jaguar> Sender: kvm-owner@vger.kernel.org List-ID: On 05/07/2011 09:50 AM, Pekka Enberg wrote: > On Sat, 2011-05-07 at 08:14 -0500, Anthony Liguori wrote: >> It seems like this patch is simply avoiding raising the interrupt line >> if the ISR has not been acknowledged yet. I don't think there's a >> functional issue here but I'm surprised that it's a win. There should >> be a very short window when the interrupt is lowered in the APIC but >> still not acknowledged in the ISR. >> >> You should just be saving a pretty cheap system call. I wonder if the >> system call is taking longer than it should.. > > The patch seems to fix a bug where the guest kernel breaks down under > interrupt storm and stops doing VIRTIO_PCI_QUEUE_NOTIFY. We assumed it > was something with our code but your comments make me wonder if there's > a real problem in KVM_IRQ_LINE. Stops doing it for a short period of time or entirely? Regards, Anthony Liguori > Pekka >