Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760412Ab2FHOjk (ORCPT ); Fri, 8 Jun 2012 10:39:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:65050 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751799Ab2FHOji (ORCPT ); Fri, 8 Jun 2012 10:39:38 -0400 Date: Fri, 8 Jun 2012 17:39:27 +0300 From: "Michael S. Tsirkin" To: Jan Kiszka Cc: Thomas Gleixner , Avi Kivity , Alex Williamson , "kvm@vger.kernel.org" , "mtosatti@redhat.com" , "linux-kernel@vger.kernel.org" , "yongjie.ren@intel.com" Subject: Re: [PATCH] KVM: Use IRQF_ONESHOT for assigned device MSI interrupts Message-ID: <20120608143927.GA4949@redhat.com> References: <20120601161521.26935.25606.stgit@bling.home> <4FC8F042.5050600@siemens.com> <1338570192.23475.25.camel@bling.home> <4FC8F867.7080103@siemens.com> <1338573558.23475.41.camel@bling.home> <4FC90961.8030701@siemens.com> <4FCB2359.9020505@redhat.com> <4FCC9EAC.9090007@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FCC9EAC.9090007@siemens.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2639 Lines: 76 On Mon, Jun 04, 2012 at 01:40:28PM +0200, Jan Kiszka wrote: > On 2012-06-04 13:21, Thomas Gleixner wrote: > > On Sun, 3 Jun 2012, Avi Kivity wrote: > > > >> On 06/01/2012 09:26 PM, Jan Kiszka wrote: > >>> > >>>> you suggesting we need a request_edge_threaded_only_irq() API? Thanks, > >>> > >>> I'm just wondering if that restriction for threaded IRQs is really > >>> necessary for all use cases we have. Threaded MSIs do not appear to me > >>> like have to be handled that conservatively, but maybe I'm missing some > >>> detail. > >>> > >> > >> btw, I'm hoping we can unthread assigned MSIs. If the delivery is > >> unicast, we can precalculate everything and all the handler has to do is > >> set the IRR, KVM_REQ_EVENT, and kick the vcpu. All of these can be done > >> from interrupt context with just RCU locking. > > > > There is really no need to run MSI/MSI-X interrupts threaded for > > KVM. I'm running the patch below for quite some time and it works like > > a charm. > > > > Thanks, > > > > tglx > > ---- .... > > This may work in practice but has two conceptual problems: > - we do not want to run a potential broadcast to all VCPUs to run in > a host IRQ handler I'm not sure why this one is a problem: injecting an interrupt once you know the vcpu seems really cheap. It's true that scanning vcpus might take a bit more time when there are lots of them but it's a single linear scan that we do anyway. And we also inject msi from irqfd callback with interrupts disabled which seems equivalent. Pls correct me if I'm wrong. > - crazy user space could have configured the route to end up in the > PIC or IOAPIC, and both are not hard-IRQ safe (this should probably > be caught on setup) Yes this needs to be fixed up. > So this shortcut requires some checks before being applied to a specific > MSI/MSI-X vector. > > > Taking KVM aside, my general question remains if threaded MSI handlers > of all devices really need to apply IRQF_ONESHOT though they should have > no use for it. > > Jan > > -- > Siemens AG, Corporate Technology, CT T DE IT 1 > Corporate Competence Center Embedded Linux > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/