From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Yang, Sheng" Subject: Re: Remaining passthrough/VT-d tasks list Date: Wed, 24 Sep 2008 17:43:01 +0800 Message-ID: <200809241743.02566.sheng.yang@intel.com> References: <0122C7C995D32147B66BF4F440D3016301C49E61@pdsmsx415.ccr.corp.intel.com> <200809241708.31835.sheng.yang@intel.com> <48DA06ED.9090605@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: "Han, Weidong" , "kvm@vger.kernel.org" , Amit Shah , "benami@il.ibm.com" , "muli@il.ibm.com" , "Kay, Allen M" , "Zhang, Xiantao" To: Avi Kivity Return-path: Received: from mga03.intel.com ([143.182.124.21]:20942 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751602AbYIXJm2 (ORCPT ); Wed, 24 Sep 2008 05:42:28 -0400 In-Reply-To: <48DA06ED.9090605@redhat.com> Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: On Wednesday 24 September 2008 17:22:53 Avi Kivity wrote: > Yang, Sheng wrote: > >> We only have three pci interrupts at this point (though this could be > >> easily extended); if you start the guest with a non-trivial number of > >> devices, you will have shared guest interrupts. > >> > >> (of course, when I pointed this out during review, people said it could > >> be done later, then forgot all about it) > > > > ..... > > > > I think it's a performance issue, not break it? How about do it like Xen > > side? Try best to avoid the share, extended the pci interrupts, improve > > hash algorithm. Is there anything else we can do? > > Two separate issues: > > 1. only three guest pci interrupts > > That's a performance issue, not correctness. can be fixed by using gsi > 16-23 in APIC mode, and by adding another IOAPIC (so we can use gsi > 16-47). Anthony Xu posted some patches for this, not sure where this > stands, but it was the right approach. > > 2. shared guest pci interrupts > > That's a correctness issue. No matter how many interrupts we have, we > may have sharing issues. Of course with only three the issue is very > pressing since we will get sharing with just a few devices. Currently > if two assigned devices share a guest interrupts, or if an emulated > device shares an interrupt with an assigned device, things will break. > > They need to be fixed independently. About the second issue, I don't understand how it would break... Would you please give more details on this? It's a QEmu bug or IOAPIC bug? -- regards Yang, Sheng