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 B1BF6C433EF for ; Fri, 25 Mar 2022 11:16:22 +0000 (UTC) Received: from localhost ([::1]:55624 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nXhvZ-0001c5-N9 for qemu-devel@archiver.kernel.org; Fri, 25 Mar 2022 07:16:21 -0400 Received: from eggs.gnu.org ([209.51.188.92]:38058) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nXhu7-0000oT-Sm for qemu-devel@nongnu.org; Fri, 25 Mar 2022 07:14:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:51015) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nXhu1-0005AE-65 for qemu-devel@nongnu.org; Fri, 25 Mar 2022 07:14:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1648206883; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=O6k1TyO4dOBTdwDpcHa7ot4pt6EtsJlzHX386NRWDeA=; b=jCzrw62K0Mnyvs+mPPfMYaVRqmmycjaVs+7tlRU6gfA+83rmeQOiRyxi7oOHIAWuR3gDrT htkyIBq7Qky/hF2pTJSQ5qW3iJjLTvJbwf6b7jDVNxIk5fa4krhzJ4c2ZdB9RRFiMFuPpE FZqSJDhCnB0u7LUk0i8uSe8hg39MFJQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-528-9AHUuN2uPYefshgF2KITCQ-1; Fri, 25 Mar 2022 07:14:17 -0400 X-MC-Unique: 9AHUuN2uPYefshgF2KITCQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DDBF6811E76; Fri, 25 Mar 2022 11:14:16 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.72]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DB09C40D0166; Fri, 25 Mar 2022 11:14:15 +0000 (UTC) Date: Fri, 25 Mar 2022 11:14:13 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Claudio Fontana Subject: Re: [libvirt RFC] virFile: new VIR_FILE_WRAPPER_BIG_PIPE to improve performance Message-ID: References: <2d1248d4-ebdf-43f9-e4a7-95f586aade8e@suse.de> <7c641d9d-fffa-e21b-7ae2-12ad35c0c238@suse.de> <35da2366-99e4-7680-a1c5-46aff83d747c@suse.de> <737974fa-905c-d171-05b0-ec4df42bc762@suse.de> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.1.5 (2021-12-30) X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 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=170.10.133.124; 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?= Cc: libvir-list@redhat.com, andrea.righi@canonical.com, Jiri Denemark , "Dr. David Alan Gilbert" , qemu-devel Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Mar 25, 2022 at 11:56:44AM +0100, Claudio Fontana wrote: > Thanks Daniel, > > On 3/25/22 11:33 AM, Daniel P. Berrangé wrote: > > On Fri, Mar 18, 2022 at 02:34:29PM +0100, Claudio Fontana wrote: > >> On 3/17/22 4:03 PM, Dr. David Alan Gilbert wrote: > >>> * Claudio Fontana (cfontana@suse.de) wrote: > >>>> On 3/17/22 2:41 PM, Claudio Fontana wrote: > >>>>> On 3/17/22 11:25 AM, Daniel P. Berrangé wrote: > >>>>>> On Thu, Mar 17, 2022 at 11:12:11AM +0100, Claudio Fontana wrote: > >>>>>>> On 3/16/22 1:17 PM, Claudio Fontana wrote: > >>>>>>>> On 3/14/22 6:48 PM, Daniel P. Berrangé wrote: > >>>>>>>>> On Mon, Mar 14, 2022 at 06:38:31PM +0100, Claudio Fontana wrote: > >>>>>>>>>> On 3/14/22 6:17 PM, Daniel P. Berrangé wrote: > >>>>>>>>>>> On Sat, Mar 12, 2022 at 05:30:01PM +0100, Claudio Fontana wrote: > >>>>>>>>>>>> the first user is the qemu driver, > >>>>>>>>>>>> > >>>>>>>>>>>> virsh save/resume would slow to a crawl with a default pipe size (64k). > >>>>>>>>>>>> > >>>>>>>>>>>> This improves the situation by 400%. > >>>>>>>>>>>> > >>>>>>>>>>>> Going through io_helper still seems to incur in some penalty (~15%-ish) > >>>>>>>>>>>> compared with direct qemu migration to a nc socket to a file. > >>>>>>>>>>>> > >>>>>>>>>>>> Signed-off-by: Claudio Fontana > >>>>>>>>>>>> --- > >>>>>>>>>>>> src/qemu/qemu_driver.c | 6 +++--- > >>>>>>>>>>>> src/qemu/qemu_saveimage.c | 11 ++++++----- > >>>>>>>>>>>> src/util/virfile.c | 12 ++++++++++++ > >>>>>>>>>>>> src/util/virfile.h | 1 + > >>>>>>>>>>>> 4 files changed, 22 insertions(+), 8 deletions(-) > >>>>>>>>>>>> > >>>>>>>>>>>> Hello, I initially thought this to be a qemu performance issue, > >>>>>>>>>>>> so you can find the discussion about this in qemu-devel: > >>>>>>>>>>>> > >>>>>>>>>>>> "Re: bad virsh save /dev/null performance (600 MiB/s max)" > >>>>>>>>>>>> > >>>>>>>>>>>> https://lists.gnu.org/archive/html/qemu-devel/2022-03/msg03142.html > >>>>>> > >>>>>> > >>>>>>> Current results show these experimental averages maximum throughput > >>>>>>> migrating to /dev/null per each FdWrapper Pipe Size (as per QEMU QMP > >>>>>>> "query-migrate", tests repeated 5 times for each). > >>>>>>> VM Size is 60G, most of the memory effectively touched before migration, > >>>>>>> through user application allocating and touching all memory with > >>>>>>> pseudorandom data. > >>>>>>> > >>>>>>> 64K: 5200 Mbps (current situation) > >>>>>>> 128K: 5800 Mbps > >>>>>>> 256K: 20900 Mbps > >>>>>>> 512K: 21600 Mbps > >>>>>>> 1M: 22800 Mbps > >>>>>>> 2M: 22800 Mbps > >>>>>>> 4M: 22400 Mbps > >>>>>>> 8M: 22500 Mbps > >>>>>>> 16M: 22800 Mbps > >>>>>>> 32M: 22900 Mbps > >>>>>>> 64M: 22900 Mbps > >>>>>>> 128M: 22800 Mbps > >>>>>>> > >>>>>>> This above is the throughput out of patched libvirt with multiple Pipe Sizes for the FDWrapper. > >>>>>> > >>>>>> Ok, its bouncing around with noise after 1 MB. So I'd suggest that > >>>>>> libvirt attempt to raise the pipe limit to 1 MB by default, but > >>>>>> not try to go higher. > >>>>>> > >>>>>>> As for the theoretical limit for the libvirt architecture, > >>>>>>> I ran a qemu migration directly issuing the appropriate QMP > >>>>>>> commands, setting the same migration parameters as per libvirt, > >>>>>>> and then migrating to a socket netcatted to /dev/null via > >>>>>>> {"execute": "migrate", "arguments": { "uri", "unix:///tmp/netcat.sock" } } : > >>>>>>> > >>>>>>> QMP: 37000 Mbps > >>>>>> > >>>>>>> So although the Pipe size improves things (in particular the > >>>>>>> large jump is for the 256K size, although 1M seems a very good value), > >>>>>>> there is still a second bottleneck in there somewhere that > >>>>>>> accounts for a loss of ~14200 Mbps in throughput. > >>>> > >>>> > >>>> Interesting addition: I tested quickly on a system with faster cpus and larger VM sizes, up to 200GB, > >>>> and the difference in throughput libvirt vs qemu is basically the same ~14500 Mbps. > >>>> > >>>> ~50000 mbps qemu to netcat socket to /dev/null > >>>> ~35500 mbps virsh save to /dev/null > >>>> > >>>> Seems it is not proportional to cpu speed by the looks of it (not a totally fair comparison because the VM sizes are different). > >>> > >>> It might be closer to RAM or cache bandwidth limited though; for an extra copy. > >> > >> I was thinking about sendfile(2) in iohelper, but that probably can't work as the input fd is a socket, I am getting EINVAL. > >> > >> One thing that I noticed is: > >> > >> ommit afe6e58aedcd5e27ea16184fed90b338569bd042 > >> Author: Jiri Denemark > >> Date: Mon Feb 6 14:40:48 2012 +0100 > >> > >> util: Generalize virFileDirectFd > >> > >> virFileDirectFd was used for accessing files opened with O_DIRECT using > >> libvirt_iohelper. We will want to use the helper for accessing files > >> regardless on O_DIRECT and thus virFileDirectFd was generalized and > >> renamed to virFileWrapperFd. > >> > >> > >> And in particular the comment in src/util/virFile.c: > >> > >> /* XXX support posix_fadvise rather than O_DIRECT, if the kernel support > >> * for that is decent enough. In that case, we will also need to > >> * explicitly support VIR_FILE_WRAPPER_NON_BLOCKING since > >> * VIR_FILE_WRAPPER_BYPASS_CACHE alone will no longer require spawning > >> * iohelper. > >> */ > >> > >> by Jiri Denemark. > >> > >> I have lots of questions here, and I tried to involve Jiri and Andrea Righi here, who a long time ago proposed a POSIX_FADV_NOREUSE implementation. > >> > >> 1) What is the reason iohelper was introduced? > > > > With POSIX you can't get sensible results from poll() on FDs associated with > > plain files. It will always report the file as readable/writable, and the > > userspace caller will get blocked any time the I/O operation causes the > > kernel to read/write from the underlying (potentially very slow) storage. > > > > IOW if you give QEMU an FD associated with a plain file and tell it to > > migrate to that, the guest OS will get stalled. > > we send a stop command to qemu just before migrating to a file in virsh save though right? > With virsh restore we also first load the VM, and only then start executing it. > > So for virsh save and virsh restore, this should not be a problem? Still we need the iohelper? The same code is used in libvirt for other commands like 'virsh dump' and snapshots, where the VM remains live though. In general I don't think we should remove the iohelper, because QEMU code is written from the POV that the channels honour O_NOBLOCK. 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 :|