From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57704) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z4jRF-00022Y-8m for qemu-devel@nongnu.org; Tue, 16 Jun 2015 01:29:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z4jRC-0003Zs-2q for qemu-devel@nongnu.org; Tue, 16 Jun 2015 01:29:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50579) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z4jRB-0003Zi-Ub for qemu-devel@nongnu.org; Tue, 16 Jun 2015 01:29:30 -0400 Message-ID: <557FB435.1030202@redhat.com> Date: Tue, 16 Jun 2015 13:29:25 +0800 From: Jason Wang MIME-Version: 1.0 References: <55791F29.6060000@redhat.com> <5579228E.1040705@redhat.com> <20150611123433-mutt-send-email-mst@redhat.com> <20150611141135-mutt-send-email-mst@redhat.com> <557A9075.5030409@redhat.com> <20150612162720-mutt-send-email-mst@redhat.com> <557E8211.1050606@redhat.com> <20150615103617-mutt-send-email-mst@redhat.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 2/2] vhost user: Add RARP injection for legacy guest List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Thibaut Collet , "Michael S. Tsirkin" Cc: qemu-devel , Stefan Hajnoczi On 06/15/2015 08:12 PM, Thibaut Collet wrote: > After a resume operation the guest always kicks the backend for each > virtual queues. > A live migration does a suspend operation on the old host and a resume > operation on the new host. So the backend has a kick after migration. > > I have checked this point with a legacy guest (redhat 6-5 with kernel > version 2.6.32-431.29.2) and the kick occurs after migration or > resume. > > Jason have you an example of legacy guest that will not kick the > virtual queue after a resume ? I must miss something but migration should be transparent to guest. Could you show me the code that guest does the kick after migration? > > On Mon, Jun 15, 2015 at 10:44 AM, Michael S. Tsirkin wrote: >> On Mon, Jun 15, 2015 at 03:43:13PM +0800, Jason Wang wrote: >>> >>> On 06/12/2015 10:28 PM, Michael S. Tsirkin wrote: >>>> On Fri, Jun 12, 2015 at 03:55:33PM +0800, Jason Wang wrote: >>>>> On 06/11/2015 08:13 PM, Michael S. Tsirkin wrote: >>>>>> On Thu, Jun 11, 2015 at 02:10:48PM +0200, Thibaut Collet wrote: >>>>>>> I am not sure to understand your remark: >>>>>>> >>>>>>>> It needs to be sent when backend is activated by guest kick >>>>>>>> (in case of virtio 1, it's possible to use DRIVER_OK for this). >>>>>>>> This does not happen when VM still runs on source. >>>>>>> Could you confirm rarp can be sent by backend when the >>>>>>> VHOST_USER_SET_VRING_KICK message is received by the backend ? >>>>>> No - the time to send pakets is when you start processing >>>>>> the rings. >>>>>> >>>>>> And the time to do that is when you detect a kick on >>>>>> an eventfd, not when said fd is set. >>>>>> >>>>> Probably not. What if guest is only doing receiving? >>>> Clarification: the kick can be on any VQs. >>>> In your example, guest kicks after adding receive buffers. >>> Yes, but refill only happens on we are lacking of receive buffers. It is >>> not guaranteed to happen just after migration, we may have still have >>> enough rx buffers for device to receive. >> I think we also kick the backend after migration, do we not? >> Further, DRIVER_OK can be used as a signal to start backend too. >> >>>>> In this case, you >>>>> won't detect any kick if you don't send the rarp first.