* Claudio Fontana (cfont...@suse.de) wrote: > On 4/5/22 10:35 AM, Dr. David Alan Gilbert wrote: > > * Claudio Fontana (cfont...@suse.de) wrote: > >> On 3/28/22 10:31 AM, Daniel P. Berrangé wrote: > >>> On Sat, Mar 26, 2022 at 04:49:46PM +0100, Claudio Fontana wrote: > >>>> On 3/25/22 12:29 PM, 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 (cfont...@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 <cfont...@suse.de> > >>>>>>>>>>>>>>>> --- > >>>>>>>>>>>>>>>> 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. > >>>>> > >>>>> Yep, sendfile() requires the input to be a mmapable FD, > >>>>> and the output to be a socket. > >>>>> > >>>>> Try splice() instead which merely requires 1 end to be a > >>>>> pipe, and the other end can be any FD afaik. > >>>>> > >>>> > >>>> I did try splice(), but performance is worse by around 500%. > >>> > >>> Hmm, that's certainly unexpected ! > >>> > >>>> Any ideas welcome, > >>> > >>> I learnt there is also a newer copy_file_range call, not sure if that's > >>> any better. > >>> > >>> You passed len as 1 MB, I wonder if passing MAXINT is viable ? We just > >>> want to copy everything IIRC. > >>> > >>> With regards, > >>> Daniel > >>> > >> > >> Crazy idea, would trying to use the parallel migration concept for > >> migrating to/from a file make any sense? > >> > >> Not sure if applying the qemu multifd implementation of this would apply, > >> maybe it could be given another implementation for "toFile", trying to use > >> more than one cpu to do the transfer? > > > > I can't see a way that would help; well, I could if you could > > somehow have multiple io helper threads that dealt with it. > > The first issue I encounter here for both the "virsh save" and "virsh > restore" scenarios is that libvirt uses fd: migration, not unix: migration. > QEMU supports multifd for unix:, tcp:, vsock: as far as I can see. > > Current save procedure in QMP in short: > > {"execute":"migrate-set-capabilities", ...} > {"execute":"migrate-set-parameters", ...} > {"execute":"getfd","arguments":{"fdname":"migrate"}, ...} fd=26 > QEMU_MONITOR_IO_SEND_FD: fd=26 > {"execute":"migrate","arguments":{"uri":"fd:migrate"}, ...} > > > Current restore procedure in QMP in short: > > (start QEMU) > {"execute":"migrate-incoming","arguments":{"uri":"fd:21"}, ...} > > > Should I investigate changing libvirt to use unix: for save/restore? > Or should I look into changing qemu to somehow accept fd: for multifd, > meaning I guess providing multiple fd: uris in the migrate command?
So I'm not sure this is the right direction; i.e. if multifd is the right answer to your problem. However, I think the qemu code probably really really wants to be a socket. Dave > > Thank you for your help, > > Claudio > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
