From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030353Ab2HPSWP (ORCPT ); Thu, 16 Aug 2012 14:22:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33557 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030311Ab2HPSWK (ORCPT ); Thu, 16 Aug 2012 14:22:10 -0400 Message-ID: <502D1FF4.20506@redhat.com> Date: Thu, 16 Aug 2012 19:29:40 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: "Michael S. Tsirkin" CC: Alex Williamson , gleb@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v8 0/6] kvm: level irqfd support References: <20120810223633.809.44188.stgit@bling.home> <20120815142803.GF3068@redhat.com> <1345052191.4683.435.camel@ul30vt.home> <20120815192224.GB5670@redhat.com> In-Reply-To: <20120815192224.GB5670@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/15/2012 10:22 PM, Michael S. Tsirkin wrote: > On Wed, Aug 15, 2012 at 11:36:31AM -0600, Alex Williamson wrote: >> On Wed, 2012-08-15 at 17:28 +0300, Michael S. Tsirkin wrote: >> > On Fri, Aug 10, 2012 at 04:37:08PM -0600, Alex Williamson wrote: >> > > v8: >> > > >> > > Trying a new approach. Nobody seems to like the internal IRQ >> > > source ID object and the interactions it implies between irqfd >> > > and eoifd, so let's get rid of it. Instead, simply expose >> > > IRQ source IDs to userspace. This lets the user be in charge >> > > of freeing them or hanging onto a source ID for later use. >> > >> > In the end it turns out source ID is an optimization for shared >> > interrupts, isn't it? Can't we apply the optimization transparently to >> > the user? E.g. if we have some spare source IDs, allocate them, if we >> > run out, use a shared source ID? >> >> Let's think about shared source IDs a bit more. I think it's wrong that >> irqfd uses KVM_USERSPACE_IRQ_SOURCE_ID, but I'm questioning whether all >> irqfd users can share a source ID. We do not get the logical OR of all >> users by putting them on the same source ID, we get "last set wins". >> KVM_USERSPACE_IRQ_SOURCE_ID is used for multiple inputs because the >> logical OR happens in userspace. How would we not starve a user if we >> define KVM_IRQFD_SOURCE_ID? What am I missing? > > That all irqfds are deasserted on EOI anyway. So there's no point > to do a logical OR. > > What if a level irqfd shares a line with a KVM_IRQ_LINE ioctl? Then an EOI can de-assert the irqfd source, but the line is kept high by the last KVM_IRQ_LINE invocation. -- error compiling committee.c: too many arguments to function