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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id A408DC433EF for ; Wed, 9 Mar 2022 18:48:51 +0000 (UTC) Received: from localhost ([::1]:60564 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nS1Mg-0002eE-JQ for qemu-devel@archiver.kernel.org; Wed, 09 Mar 2022 13:48:50 -0500 Received: from eggs.gnu.org ([209.51.188.92]:41068) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nS1KB-0000i7-Ih for qemu-devel@nongnu.org; Wed, 09 Mar 2022 13:46:15 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:41373) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nS1K9-0000kB-7Y for qemu-devel@nongnu.org; Wed, 09 Mar 2022 13:46:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646851572; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fNtUUWVxuCevFb4hBpSa5C1sFtd7QXBf0PrQYBldgio=; b=Oe8kdxUwDhcZeAL0A9XUkjZfzAyD4miIJTrILj9IxkSQQY/8eAeHB5hD/r3GbY81jryGLN jL78G+x6vRI4jfBf4vaaYVODKHwXmh9fTQNaWcb8yiGl9o70b3uZ3wj4WMVWb8XqjMBx4J QLFipgcMp7op5P9uGrB0SeHx48Fn7qc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-499-HNoLJHcjPB-izi-VrCFcMg-1; Wed, 09 Mar 2022 13:46:11 -0500 X-MC-Unique: HNoLJHcjPB-izi-VrCFcMg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 41CD451DC; Wed, 9 Mar 2022 18:46:10 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.177]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B790E8478F; Wed, 9 Mar 2022 18:46:08 +0000 (UTC) Date: Wed, 9 Mar 2022 18:46:05 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Claudio Fontana , Jim Fehlig , Juan Quintela , "Dr. David Alan Gilbert" , qemu-devel Subject: Re: bad virsh save /dev/null performance (600 MiB/s max) Message-ID: References: <5f318297-51c0-366b-758b-733ba27684ba@suse.de> <5b3d17d2-f07f-8cb1-54ff-6a517dc4eaef@suse.de> <51b486fc-2c71-e1c6-6412-d462234d67fb@suse.de> <700779ea-4274-7872-6022-d32457a00160@suse.de> <47786b29-b1a2-1f6a-568d-b61398e0f641@suse.de> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Mar 09, 2022 at 06:37:42PM +0000, Daniel P. Berrangé wrote: > On Wed, Mar 09, 2022 at 07:27:12PM +0100, Claudio Fontana wrote: > > > > One difference I could see looking at the qmp commands issued by libvirt in the "virsh save" case, > > is "detach:true" in the migration command (which seems to have no effect in qemu), > > That is a bug in libvirt - it should not be setting that in QMP. > > To quote the QAPI spec for 'migrate' > > # @detach: this argument exists only for compatibility reasons and > # is ignored by QEMU > > > > > > > > and maybe more interestingly this stuff about the "fd": > > > > > > 2022-03-09 17:29:34.247+0000: 20390: info : qemuMonitorSend:995 : QEMU_MONITOR_SEND_MSG: mon=0x7faa9003ebf0 msg={"execute":"getfd","arguments":{"fdname":"migrate"},"id":"libvirt-390"}^M > > fd=34 > > 2022-03-09 17:29:34.247+0000: 20387: info : qemuMonitorIOWrite:452 : QEMU_MONITOR_IO_WRITE: mon=0x7faa9003ebf0 buf={"execute":"getfd","arguments":{"fdname":"migrate"},"id":"libvirt-390"}^M > > len=73 ret=73 errno=0 > > 2022-03-09 17:29:34.247+0000: 20387: info : qemuMonitorIOWrite:457 : QEMU_MONITOR_IO_SEND_FD: mon=0x7faa9003ebf0 fd=34 ret=73 errno=0 > > 2022-03-09 17:29:34.248+0000: 20387: info : qemuMonitorJSONIOProcessLine:240 : QEMU_MONITOR_RECV_REPLY: mon=0x7faa9003ebf0 reply={"return": {}, "id": "libvirt-390"} > > 2022-03-09 17:29:34.249+0000: 20390: info : qemuMonitorSend:995 : QEMU_MONITOR_SEND_MSG: mon=0x7faa9003ebf0 msg={"execute":"migrate","arguments":{"detach":true,"blk":false,"inc":false,"uri":"fd:migrate"},"id":"libvirt-391"}^M > > fd=-1 > > 2022-03-09 17:29:34.249+0000: 20387: info : qemuMonitorIOWrite:452 : QEMU_MONITOR_IO_WRITE: mon=0x7faa9003ebf0 buf={"execute":"migrate","arguments":{"detach":true,"blk":false,"inc":false,"uri":"fd:migrate"},"id":"libvirt-391"}^M > > len=113 ret=113 errno=0 > > > > > > in qemu I am currently looking at the code in migration/socket.c > > vs the code in migration/fd.c , wonder if the difference would > > stem from there.. > > When saving to a file, libvirt passes in a pre-opened FD for > QEU to use. IIRC this should always be a pipe FD connected to > libvirt's iohelper program, sometimes indirectly via a compression > program. It occurs to me that pipes and sockets likely use very different buffer sizes, with sockets larger IIUC, and buffer sizes can impact throughput. Could be worth exploring a change to libvirt code to use socketpair() instead of pipe() to see if it impacts performance in any meaningful way, or playing with fcntl(F_SETPIPE_SZ) With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|