From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56503) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f6G0B-0003GS-BO for qemu-devel@nongnu.org; Wed, 11 Apr 2018 09:41:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f6G07-0007oy-Cy for qemu-devel@nongnu.org; Wed, 11 Apr 2018 09:41:31 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:37332 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 1f6G07-0007oT-8i for qemu-devel@nongnu.org; Wed, 11 Apr 2018 09:41:27 -0400 References: <20180411072027.5656-1-tiwei.bie@intel.com> <20180411083853.qa6y6zevjpvamrdx@debian> From: Jason Wang Message-ID: Date: Wed, 11 Apr 2018 21:41:05 +0800 MIME-Version: 1.0 In-Reply-To: <20180411083853.qa6y6zevjpvamrdx@debian> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [RFC] vhost-user: introduce F_NEED_ALL_IOTLB protocol feature List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Tiwei Bie Cc: mst@redhat.com, cunming.liang@intel.com, qemu-devel@nongnu.org, peterx@redhat.com, zhihong.wang@intel.com, dan.daly@intel.com On 2018=E5=B9=B404=E6=9C=8811=E6=97=A5 16:38, Tiwei Bie wrote: > On Wed, Apr 11, 2018 at 04:01:19PM +0800, Jason Wang wrote: >> On 2018=E5=B9=B404=E6=9C=8811=E6=97=A5 15:20, Tiwei Bie wrote: >>> This patch introduces VHOST_USER_PROTOCOL_F_NEED_ALL_IOTLB >>> feature for vhost-user. By default, vhost-user backend needs >>> to query the IOTLBs from QEMU after meeting unknown IOVAs. >>> With this protocol feature negotiated, QEMU will provide all >>> the IOTLBs to vhost-user backend without waiting for the >>> queries from backend. This is helpful when using a hardware >>> accelerator which is not able to handle unknown IOVAs at the >>> vhost-user backend. >>> >>> Signed-off-by: Tiwei Bie >>> --- >>> The idea of this patch is to let QEMU push all the IOTLBs >>> to vhost-user backend without waiting for the queries from >>> the backend. Because hardware accelerator at the vhost-user >>> backend may not be able to handle unknown IOVAs. >>> >>> This is just a RFC for now. It seems that, it doesn't work >>> as expected when guest is using kernel driver (To handle >>> this case, it seems that some RAM regions' events also need >>> to be listened). Any comments would be appreciated! Thanks! >> Interesting, a quick question is why this is needed? Can we just use e= xist >> IOTLB update message? > Yeah, we are still using the existing IOTLB update messages > to send the IOTLB messages to backend. The only difference > is that, QEMU won't wait for the queries before sending the > IOTLB update messages. Yes, my question is not very clear. I mean why must need a new feature=20 bit? It looks to me qemu code can work without this. Thanks > >> It looks to me at least kernel does not need this. > Something similar in kernel vhost is that, for kernel vhost, > QEMU needs to push the IOTLBs of some ring addrs to kernel > vhost backend without waiting for the queries. > > Best regards, > Tiwei Bie > >> Thanks