From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756290AbbLQOjP (ORCPT ); Thu, 17 Dec 2015 09:39:15 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:37938 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755421AbbLQOjO (ORCPT ); Thu, 17 Dec 2015 09:39:14 -0500 Date: Thu, 17 Dec 2015 15:39:10 +0100 From: Peter Zijlstra To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Jason Wang , qemu-devel@nongnu.org, Alexander Duyck Subject: Re: [PATCH] virtio_ring: use smp_store_mb Message-ID: <20151217143910.GD6344@twins.programming.kicks-ass.net> References: <1450347932-16325-1-git-send-email-mst@redhat.com> <20151217105238.GA6375@twins.programming.kicks-ass.net> <20151217131554-mutt-send-email-mst@redhat.com> <20151217135726.GA6344@twins.programming.kicks-ass.net> <20151217161124-mutt-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151217161124-mutt-send-email-mst@redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 17, 2015 at 04:33:44PM +0200, Michael S. Tsirkin wrote: > On Thu, Dec 17, 2015 at 02:57:26PM +0100, Peter Zijlstra wrote: > > > > You could of course go fix that instead of mutilating things into > > sort-of functional state. > > Yes, we'd just need to touch all architectures, all for > the sake of UP which almost no one uses. > Basically, we need APIs that explicitly are > for talking to another kernel on a different CPU on > the same SMP system, and implemented identically > between CONFIG_SMP and !CONFIG_SMP on all architectures. > > Do you think this is something of general usefulness, > outside virtio? I'm not aware of any other case, but if there are more parts of virt that need this then I see no problem adding it. That is, virt in general is the only use-case that I can think of, because this really is an artifact of interfacing with an SMP host while running an UP kernel. But I'm really not familiar with virt, so I do not know if there's more sites outside of virtio that could use this. Touching all archs is a tad tedious, but its fairly straight forward. From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52018) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a9ZiB-0007Rc-H4 for qemu-devel@nongnu.org; Thu, 17 Dec 2015 09:39:20 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a9Zi6-00071Q-D6 for qemu-devel@nongnu.org; Thu, 17 Dec 2015 09:39:19 -0500 Received: from bombadil.infradead.org ([2001:1868:205::9]:55314) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a9Zi6-00071H-7G for qemu-devel@nongnu.org; Thu, 17 Dec 2015 09:39:14 -0500 Date: Thu, 17 Dec 2015 15:39:10 +0100 From: Peter Zijlstra Message-ID: <20151217143910.GD6344@twins.programming.kicks-ass.net> References: <1450347932-16325-1-git-send-email-mst@redhat.com> <20151217105238.GA6375@twins.programming.kicks-ass.net> <20151217131554-mutt-send-email-mst@redhat.com> <20151217135726.GA6344@twins.programming.kicks-ass.net> <20151217161124-mutt-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151217161124-mutt-send-email-mst@redhat.com> Subject: Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, Jason Wang , linux-kernel@vger.kernel.org, Alexander Duyck , virtualization@lists.linux-foundation.org On Thu, Dec 17, 2015 at 04:33:44PM +0200, Michael S. Tsirkin wrote: > On Thu, Dec 17, 2015 at 02:57:26PM +0100, Peter Zijlstra wrote: > > > > You could of course go fix that instead of mutilating things into > > sort-of functional state. > > Yes, we'd just need to touch all architectures, all for > the sake of UP which almost no one uses. > Basically, we need APIs that explicitly are > for talking to another kernel on a different CPU on > the same SMP system, and implemented identically > between CONFIG_SMP and !CONFIG_SMP on all architectures. > > Do you think this is something of general usefulness, > outside virtio? I'm not aware of any other case, but if there are more parts of virt that need this then I see no problem adding it. That is, virt in general is the only use-case that I can think of, because this really is an artifact of interfacing with an SMP host while running an UP kernel. But I'm really not familiar with virt, so I do not know if there's more sites outside of virtio that could use this. Touching all archs is a tad tedious, but its fairly straight forward. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH] virtio_ring: use smp_store_mb Date: Thu, 17 Dec 2015 15:39:10 +0100 Message-ID: <20151217143910.GD6344@twins.programming.kicks-ass.net> References: <1450347932-16325-1-git-send-email-mst@redhat.com> <20151217105238.GA6375@twins.programming.kicks-ass.net> <20151217131554-mutt-send-email-mst@redhat.com> <20151217135726.GA6344@twins.programming.kicks-ass.net> <20151217161124-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20151217161124-mutt-send-email-mst@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, Alexander Duyck , virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Thu, Dec 17, 2015 at 04:33:44PM +0200, Michael S. Tsirkin wrote: > On Thu, Dec 17, 2015 at 02:57:26PM +0100, Peter Zijlstra wrote: > > > > You could of course go fix that instead of mutilating things into > > sort-of functional state. > > Yes, we'd just need to touch all architectures, all for > the sake of UP which almost no one uses. > Basically, we need APIs that explicitly are > for talking to another kernel on a different CPU on > the same SMP system, and implemented identically > between CONFIG_SMP and !CONFIG_SMP on all architectures. > > Do you think this is something of general usefulness, > outside virtio? I'm not aware of any other case, but if there are more parts of virt that need this then I see no problem adding it. That is, virt in general is the only use-case that I can think of, because this really is an artifact of interfacing with an SMP host while running an UP kernel. But I'm really not familiar with virt, so I do not know if there's more sites outside of virtio that could use this. Touching all archs is a tad tedious, but its fairly straight forward.