From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark McLoughlin Subject: Re: [KVM PATCH v4 3/3] kvm: add iosignalfd support Date: Wed, 27 May 2009 17:25:44 +0000 Message-ID: <1243445144.16318.15.camel@blaa> References: <20090526191010.20860.75372.stgit@dev.haskins.net> <20090526191539.20860.1385.stgit@dev.haskins.net> <4A1D01F8.8080508@redhat.com> <4A1D285C.9050008@novell.com> <4A1D2DD8.2050709@redhat.com> Reply-To: Mark McLoughlin Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Gregory Haskins , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Davide Libenzi , mtosatti@redhat.com To: Avi Kivity Return-path: Received: from mx2.redhat.com ([66.187.237.31]:37188 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756021AbZE0RZs (ORCPT ); Wed, 27 May 2009 13:25:48 -0400 In-Reply-To: <4A1D2DD8.2050709@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, 2009-05-27 at 15:11 +0300, Avi Kivity wrote: > Multiple cookies on the same address are required by virtio. You can't > mux since the data doesn't go anywhere. > > Virtio can survive by checking all rings on a notify, and we can later > add a mechanism that has a distinct address for each ring, but let's see > if we can cope with multiple cookies. Mark? Trying to catch up, but you're talking about replacing virtio-pci QUEUE_NOTIFY handling with iosignalfd ? For a perfect replacement, what you really need is to be able to register multiple cookies per address range, but only have them trigger if the written data matches a provided value. If the data is lost, virtio has no way of knowing which queue is being notified, so we either end up with per-device, rather than per-queue, notifications (probably not too bad for net, at least) or a different notify address per queue (limiting the number of queues per device). Cheers, Mark.