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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id v2-20020adf8b42000000b001edc38024c9sm12289621wra.65.2022.03.07.04.28.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Mar 2022 04:28:16 -0800 (PST) Date: Mon, 7 Mar 2022 12:28:13 +0000 From: "Dr. David Alan Gilbert" To: Claudio Fontana Subject: Re: starting to look at qemu savevm performance, a first regression detected Message-ID: References: <8826b03d-e5e9-0e65-cab7-ea1829f48e6c@suse.de> <62ba8b1e-d641-5b10-c1b3-54b7d5a652e7@suse.de> <1f70a086-2b72-bd83-414b-476f5e6d0094@suse.de> <5f318297-51c0-366b-758b-733ba27684ba@suse.de> <5b3d17d2-f07f-8cb1-54ff-6a517dc4eaef@suse.de> MIME-Version: 1.0 In-Reply-To: <5b3d17d2-f07f-8cb1-54ff-6a517dc4eaef@suse.de> User-Agent: Mutt/2.1.5 (2021-12-30) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@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: , Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel , Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Claudio Fontana (cfontana@suse.de) wrote: > On 3/7/22 1:20 PM, Daniel P. Berrangé wrote: > > On Mon, Mar 07, 2022 at 01:09:55PM +0100, Claudio Fontana wrote: > >> On 3/7/22 1:00 PM, Daniel P. Berrangé wrote: > >>> On Mon, Mar 07, 2022 at 12:19:22PM +0100, Claudio Fontana wrote: > >>>> On 3/7/22 10:51 AM, Daniel P. Berrangé wrote: > >>>>> On Mon, Mar 07, 2022 at 10:44:56AM +0100, Claudio Fontana wrote: > >>>>>> Hello Daniel, > >>>>>> > >>>>>> On 3/7/22 10:27 AM, Daniel P. Berrangé wrote: > >>>>>>> On Sat, Mar 05, 2022 at 02:19:39PM +0100, Claudio Fontana wrote: > >>>>>>>> > >>>>>>>> Hello all, > >>>>>>>> > >>>>>>>> I have been looking at some reports of bad qemu savevm performance in large VMs (around 20+ Gb), > >>>>>>>> when used in libvirt commands like: > >>>>>>>> > >>>>>>>> > >>>>>>>> virsh save domain /dev/null > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>> I have written a simple test to run in a Linux centos7-minimal-2009 guest, which allocates and touches 20G mem. > >>>>>>>> > >>>>>>>> With any qemu version since around 2020, I am not seeing more than 580 Mb/Sec even in the most ideal of situations. > >>>>>>>> > >>>>>>>> This drops to around 122 Mb/sec after commit: cbde7be900d2a2279cbc4becb91d1ddd6a014def . > >>>>>>>> > >>>>>>>> Here is the bisection for this particular drop in throughput: > >>>>>>>> > >>>>>>>> commit cbde7be900d2a2279cbc4becb91d1ddd6a014def (HEAD, refs/bisect/bad) > >>>>>>>> Author: Daniel P. Berrangé > >>>>>>>> Date: Fri Feb 19 18:40:12 2021 +0000 > >>>>>>>> > >>>>>>>> migrate: remove QMP/HMP commands for speed, downtime and cache size > >>>>>>>> > >>>>>>>> The generic 'migrate_set_parameters' command handle all types of param. > >>>>>>>> > >>>>>>>> Only the QMP commands were documented in the deprecations page, but the > >>>>>>>> rationale for deprecating applies equally to HMP, and the replacements > >>>>>>>> exist. Furthermore the HMP commands are just shims to the QMP commands, > >>>>>>>> so removing the latter breaks the former unless they get re-implemented. > >>>>>>>> > >>>>>>>> Reviewed-by: Dr. David Alan Gilbert > >>>>>>>> Signed-off-by: Daniel P. Berrangé > >>>>>>> > >>>>>>> That doesn't make a whole lot of sense as a bisect result. > >>>>>>> How reliable is that bisect end point ? Have you bisected > >>>>>>> to that point more than once ? > >>>>>> > >>>>>> I did run through the bisect itself only once, so I'll double check that. > >>>>>> The results seem to be reproducible almost to the second though, a savevm that took 35 seconds before the commit takes 2m 48 seconds after. > >>>>>> > >>>>>> For this test I am using libvirt v6.0.0. > >>> > >>> I've just noticed this. That version of libvirt is 2 years old and > >>> doesn't have full support for migrate_set_parameters. > >>> > >>> > >>>> 2022-03-07 10:47:20.145+0000: 134386: info : qemuMonitorIOWrite:452 : QEMU_MONITOR_IO_WRITE: mon=0x7fa4380028a0 buf={"execute":"migrate_set_speed","arguments":{"value":9223372036853727232},"id":"libvirt-19"}^M > >>>> len=93 ret=93 errno=0 > >>>> 2022-03-07 10:47:20.146+0000: 134386: info : qemuMonitorJSONIOProcessLine:240 : QEMU_MONITOR_RECV_REPLY: mon=0x7fa4380028a0 reply={"id": "libvirt-19", "error": {"class": "CommandNotFound", "desc": "The command migrate_set_speed has not been found"}} > >>>> 2022-03-07 10:47:20.147+0000: 134391: error : qemuMonitorJSONCheckError:412 : internal error: unable to execute QEMU command 'migrate_set_speed': The command migrate_set_speed has not been found > >>> > >>> We see the migrate_set_speed failing and libvirt obviously ignores that > >>> failure. > >>> > >>> In current libvirt migrate_set_speed is not used as it properly > >>> handles migrate_set_parameters AFAICT. > >>> > >>> I think you just need to upgrade libvirt if you want to use this > >>> newer QEMU version > >>> > >>> Regards, > >>> Daniel > >>> > >> > >> Got it, this explains it, sorry for the noise on this. > >> > >> I'll continue to investigate the general issue of low throughput with virsh save / qemu savevm . > > > > BTW, consider measuring with the --bypass-cache flag to virsh save. > > This causes libvirt to use a I/O helper that uses O_DIRECT when > > saving the image. This should give more predictable results by > > avoiding the influence of host I/O cache which can be in a differnt > > state of usage each time you measure. It was also intended that > > by avoiding hitting cache, saving the memory image of a large VM > > will not push other useful stuff out of host I/O cache which can > > negatively impact other running VMs. > > > > Also it is possible to configure compression on the libvirt side > > which may be useful if you have spare CPU cycles, but your storage > > is slow. See 'save_image_format' in the /etc/libvirt/qemu.conf > > > > With regards, > > Daniel > > > > Hi Daniel, thanks for these good info, > > regarding slow storage, for these tests I am saving to /dev/null to avoid having to take storage into account > (and still getting low bandwidth unfortunately) so I guess compression is out of the question. What type of speeds do you get if you try a migrate to a netcat socket? Dave > Thanks! > > Claudio > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK