From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [Qemu-devel] [RFC] create a single workqueue for each vm to update vm irq routing table Date: Tue, 26 Nov 2013 16:58:53 +0100 Message-ID: <5294C53D.8060009@redhat.com> References: <52949847.6020908@redhat.com> <5294A68F.6060301@redhat.com> <5294B461.5000405@redhat.com> <5294B634.4050801@cloudius-systems.com> <20131126150357.GA20352@redhat.com> <5294BC3B.6070902@redhat.com> <5294BD61.7080904@cloudius-systems.com> <5294BE22.7040105@redhat.com> <5294BFB7.2090202@cloudius-systems.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , Avi Kivity , "Huangweidong (C)" , KVM , "Michael S. Tsirkin" , "Jinxin (F)" , "Zhanghaoyu (A)" , Luonengjun , "qemu-devel@nongnu.org" , Zanghongyong To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:58423 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932300Ab3KZP7G (ORCPT ); Tue, 26 Nov 2013 10:59:06 -0500 In-Reply-To: <5294BFB7.2090202@cloudius-systems.com> Sender: kvm-owner@vger.kernel.org List-ID: Il 26/11/2013 16:35, Avi Kivity ha scritto: >>>> If we want to ensure, we need to use a different mechanism for >>>> synchronization than the global RCU. QRCU would work; readers are not >>>> wait-free but only if there is a concurrent synchronize_qrcu, which >>>> should be rare. >>> An alternative path is to convince ourselves that the hardware does not >>> provide the guarantees that the current code provides, and so we can >>> relax them. >> No, I think it's a reasonable guarantee to provide. > > Why? Because IIUC the semantics may depend not just on the interrupt controller, but also on the specific PCI device. It seems safer to assume that at least one device/driver pair wants this to work. (BTW, PCI memory writes are posted, but configuration writes are not). Paolo