From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:55580) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gk4Ql-00049z-3a for qemu-devel@nongnu.org; Thu, 17 Jan 2019 04:57:47 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gk4Qk-0006Di-Bg for qemu-devel@nongnu.org; Thu, 17 Jan 2019 04:57:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47136) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gk4Qk-0006CY-63 for qemu-devel@nongnu.org; Thu, 17 Jan 2019 04:57:46 -0500 References: <20190109112728.9214-1-xieyongji@baidu.com> <20190109112728.9214-5-xieyongji@baidu.com> From: Jason Wang Message-ID: Date: Thu, 17 Jan 2019 17:57:29 +0800 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v4 for-4.0 4/7] libvhost-user: Support tracking inflight I/O in shared memory List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Yongji Xie Cc: "Michael S. Tsirkin" , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , "Coquelin, Maxime" , Yury Kotov , =?UTF-8?B?0JXQstCz0LXQvdC40Lkg0K/QutC+0LLQu9C10LI=?= , qemu-devel , zhangyu31@baidu.com, chaiwen@baidu.com, nixun@baidu.com, lilin24@baidu.com, Xie Yongji , Stefan Hajnoczi On 2019/1/15 =E4=B8=8B=E5=8D=8810:51, Yongji Xie wrote: >> Well, this may work but here're my points: >> >> 1) The code want to recover from backed crash by introducing extra spa= ce >> to store inflight data, but it still depends on the backend to set/get >> the inflight state >> >> 2) Since the backend could be killed at any time, the backend must hav= e >> the ability to recover from the partial inflight state >> >> So it looks to me 1) tends to be self-contradictory and 2) tends to be >> recursive. The above lines show how tricky could the code looks like. >> >> Solving this at vhost-user level through at backend is probably wrong. >> It's time to consider the support from virtio itself. >> > I agree that supporting this in virtio level may be better. For > example, resubmitting inflight I/O once DEVICE_NEEDS_RESET is set in > Stefan's proposal. But I still think QEMU should be able to provide > this ability too. Supposed that one vhost-user backend need to support > multiple VMs. We can't enable reconnect ability until all VMs' guest > driver support the new feature. It's limited. That's the way virtio evolves. > But if QEMU have the > ability to store inflight buffer, the backend could at least have a > chance to support this case. The problem is, you need a careful designed protocol described somewhere=20 (is vhost-user.txt a good place for this?). And this work will be=20 (partial) duplicated for the future support from virtio spec itself. > Maybe backend could have other way to > avoid the tricky code. I'm not sure, but it was probably not easy. Thanks > > Thanks,