From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] [RFC] create a single workqueue for each vm to update vm irq routing table Date: Tue, 26 Nov 2013 17:35:19 +0200 Message-ID: <5294BFB7.2090202@cloudius-systems.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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed 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: Paolo Bonzini Return-path: Received: from mail-bk0-f46.google.com ([209.85.214.46]:59215 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932190Ab3KZPfX (ORCPT ); Tue, 26 Nov 2013 10:35:23 -0500 Received: by mail-bk0-f46.google.com with SMTP id u15so2648882bkz.19 for ; Tue, 26 Nov 2013 07:35:22 -0800 (PST) In-Reply-To: <5294BE22.7040105@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 11/26/2013 05:28 PM, Paolo Bonzini wrote: > Il 26/11/2013 16:25, 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? From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56307) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VlKfn-0005pw-Js for qemu-devel@nongnu.org; Tue, 26 Nov 2013 10:35:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VlKfb-0003LR-5B for qemu-devel@nongnu.org; Tue, 26 Nov 2013 10:35:35 -0500 Received: from mail-bk0-f46.google.com ([209.85.214.46]:53014) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VlKfa-0003L4-VB for qemu-devel@nongnu.org; Tue, 26 Nov 2013 10:35:23 -0500 Received: by mail-bk0-f46.google.com with SMTP id u15so2669691bkz.33 for ; Tue, 26 Nov 2013 07:35:22 -0800 (PST) Message-ID: <5294BFB7.2090202@cloudius-systems.com> Date: Tue, 26 Nov 2013 17:35:19 +0200 From: Avi Kivity MIME-Version: 1.0 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> In-Reply-To: <5294BE22.7040105@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC] create a single workqueue for each vm to update vm irq routing table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: "Huangweidong (C)" , KVM , Gleb Natapov , "Michael S. Tsirkin" , "Zhanghaoyu (A)" , Luonengjun , "qemu-devel@nongnu.org" , Zanghongyong , Avi Kivity , "Jinxin (F)" On 11/26/2013 05:28 PM, Paolo Bonzini wrote: > Il 26/11/2013 16:25, 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?