From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6830CC606B4 for ; Mon, 8 Jul 2019 13:19:48 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 44F3920861 for ; Mon, 8 Jul 2019 13:19:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 44F3920861 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41654 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hkTYZ-00047y-CS for qemu-devel@archiver.kernel.org; Mon, 08 Jul 2019 09:19:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:50937) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hkTWk-0002lO-G3 for qemu-devel@nongnu.org; Mon, 08 Jul 2019 09:18:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hkTWi-0000Pd-DN for qemu-devel@nongnu.org; Mon, 08 Jul 2019 09:17:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58710) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hkTWV-0008KI-Vs; Mon, 08 Jul 2019 09:17:41 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 930B98E22C; Mon, 8 Jul 2019 13:16:50 +0000 (UTC) Received: from maximlenovopc.usersys.redhat.com (unknown [10.35.206.83]) by smtp.corp.redhat.com (Postfix) with ESMTP id 01AD42B9F5; Mon, 8 Jul 2019 13:16:46 +0000 (UTC) Message-ID: <7470cb6f1a3889015a086d340cc83ff326b9e720.camel@redhat.com> From: Maxim Levitsky To: Kevin Wolf , "wangjie (P)" Date: Mon, 08 Jul 2019 16:16:43 +0300 In-Reply-To: <20190705075053.GA5016@dhcp-200-226.str.redhat.com> References: <2b55a1d9-7c4f-c895-95fa-a32a7f63ad07@huawei.com> <20190705075053.GA5016@dhcp-200-226.str.redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 08 Jul 2019 13:16:55 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] =?utf-8?q?=5BQemu-block=5D_question=EF=BC=9Aabout_i?= =?utf-8?q?ntroduce_a_new_feature_named_=E2=80=9CI/O_hang=E2=80=9D?= X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-block@nongnu.org, "Fangyi \(C\)" , armbru@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 2019-07-05 at 09:50 +0200, Kevin Wolf wrote: > Am 04.07.2019 um 17:16 hat wangjie (P) geschrieben: > > Hi, everybody=EF=BC=9A > >=20 > > I developed a feature named "I/O hang"=EF=BC=8Cmy intention is to sol= ve the problem > > like that=EF=BC=9A > > If the backend storage media of VM disk is far-end storage like IPSAN= or > > FCSAN, storage net link will always disconnection and > > make I/O requests return EIO to Guest, and the status of filesystem i= n Guest > > will be read-only, even the link recovered > > after a while, the status of filesystem in Guest will not recover. >=20 > The standard solution for this is configuring the guest device with > werror=3Dstop,rerror=3Dstop so that the error is not delivered to the g= uest, > but the VM is stopped. When you run 'cont', the request is then retried= . >=20 > > So I developed a feature named "I/O hang" to solve this problem, the > > solution like that=EF=BC=9A > > when some I/O requests return EIO in backend, "I/O hang" will catch t= he > > requests in qemu block layer and > > insert the requests to a rehandle queue but not return EIO to Guest, = the I/O > > requests in Guest will hang but it does not lead > > Guest filesystem to be read-only, then "I/O hang" will loop to rehand= le the > > requests for a period time(ex. 5 second) until the requests > > not return EIO(when backend storage link recovered). >=20 > Letting requests hang without stopping the VM risks the guest running > into timeouts and deciding that its disk is broken. I came to say exactly this. While developing the nvme-mdev I also had this problem and due to assumpt= ions built in the block layer, you can't just let the guest wait forever for a request. Note that Linux's nvme driver does know how to retry failed requests, inc= luding these that timed out if that helps in any way. Best regards, Maxim Levitsky >=20 > As you say your "hang" and retry logic sits in the block layer, what do > you do when you encounter a bdrv_drain() request? >=20 > > In addition to the function as above, "I/O hang" also can sent event = to > > libvirt after backend storage status changed. > >=20 > > configure methods: > > 1. "I/O hang" ability can be configured for each disk as a disk attri= bute. > > 2. "I/O hang" timeout value also can be configured for each disk, whe= n > > storage link not recover in timeout value, > > "I/O hang" will disable rehandle I/O requests and return EIO to Gu= est. > >=20 > > Are you interested in the feature? I intend to push this feature to = qemu > > org, what's your opinion? >=20 > Were you aware of werror/rerror? Before we add another mechanism, we > need to be sure how the features compare, that the new mechanism > provides a significant advantage and that we keep code duplication as > low as possible. >=20 > Kevin >=20