From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41035) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f9CvL-0006hp-FN for qemu-devel@nongnu.org; Thu, 19 Apr 2018 13:00:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f9CvF-0000Lv-Lw for qemu-devel@nongnu.org; Thu, 19 Apr 2018 13:00:43 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:59466 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f9CvF-0000Lo-G9 for qemu-devel@nongnu.org; Thu, 19 Apr 2018 13:00:37 -0400 Date: Thu, 19 Apr 2018 20:00:34 +0300 From: "Michael S. Tsirkin" Message-ID: <20180419195651-mutt-send-email-mst@kernel.org> References: <20180412151232.17506-1-tiwei.bie@intel.com> <20180412151232.17506-7-tiwei.bie@intel.com> <20180418192154-mutt-send-email-mst@kernel.org> <20180419111439.i6gfhnept6wy7uzp@debian> <20180419182035-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH v3 6/6] vhost-user: support registering external host notifiers List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Liang, Cunming" Cc: Paolo Bonzini , "Bie, Tiwei" , "jasowang@redhat.com" , "alex.williamson@redhat.com" , "stefanha@redhat.com" , "qemu-devel@nongnu.org" , "virtio-dev@lists.oasis-open.org" , "Daly, Dan" , "Tan, Jianfeng" , "Wang, Zhihong" , "Wang, Xiao W" On Thu, Apr 19, 2018 at 04:52:20PM +0000, Liang, Cunming wrote: > > > > -----Original Message----- > > From: Paolo Bonzini [mailto:pbonzini@redhat.com] > > Sent: Thursday, April 19, 2018 11:52 PM > > To: Michael S. Tsirkin ; Liang, Cunming > > > > Cc: Bie, Tiwei ; jasowang@redhat.com; > > alex.williamson@redhat.com; stefanha@redhat.com; qemu-devel@nongnu.org; > > virtio-dev@lists.oasis-open.org; Daly, Dan ; Tan, Jianfeng > > ; Wang, Zhihong ; Wang, > > Xiao W > > Subject: Re: [PATCH v3 6/6] vhost-user: support registering external host > > notifiers > > > > On 19/04/2018 17:42, Michael S. Tsirkin wrote: > > >> A compiler barrier is enough on strongly-ordered memory platform. > > >> As it doesn't re-order store, PCI device won't see a stale index > > >> value. But a weakly-ordered memory needs sfence. > > > > > > Oh you are right. > > > > > > So it's only needed for non-intel platforms or when packets are in WC > > > memory then. And I don't know whether dpdk ever puts packets in WC > > > memory. > > > > > > I guess we'll cross this bridge when we get to it. > > > > Non-TSO architectures seem important... > > I'm not familiar with Non-TSO, trying to understand the difference > according to the feature set. Let's say non-TSO architectures do not > set 'weak_barriers'. Then mandatory barrier is used for software. HW > offload on that platform would choose different feature set against > software? Right. We'll need a flag for this feature for starters. It doesn't exist :) Paolo also points out that we should then add code to disallow migration between setups with and without the feature. > If it's not, essentially we're worried about live migration from a TSO to a non-TSO architectures platform? Probably not. > > > > Paolo