> -----邮件原件----- > 发件人: Dr. David Alan Gilbert <dgilb...@redhat.com> > 发送时间: 2019年7月12日 20:34 > 收件人: Lin Ma <l...@suse.com> > 抄送: qemu-devel@nongnu.org > 主题: Re: 答复: [Qemu-devel] migrate_set_speed has no effect if the guest is > using hugepages. > > * Lin Ma (l...@suse.com) wrote: > > > > > > > -----邮件原件----- > > > 发件人: Dr. David Alan Gilbert <dgilb...@redhat.com> > > > 发送时间: 2019年7月11日 18:24 > > > 收件人: Lin Ma <l...@suse.com> > > > 抄送: qemu-devel@nongnu.org > > > 主题: Re: [Qemu-devel] migrate_set_speed has no effect if the guest is > > > using hugepages. > > > > > > * Lin Ma (l...@suse.com) wrote: > > > > Hi all, > > > > > > Hi Lin, > > > > Hi Dave, > > > > > > > When I live migrate a qemu/kvm guest, If the guest is using huge > > > > pages, I found that the migrate_set_speed command had no effect > > > > during > > > stage 2. > > > > > > Can you explain what you mean by 'stage 2'? > > We know that the live migration contains 3 stages: > > Stage 1: Mark all of RAM dirty. > > Stage 2: Keep sending dirty RAM pages since last iteration Stage 3: > > Stop guest, transfer remaining dirty RAM, device state (Please refer > > to > > https://developers.redhat.com/blog/2015/03/24/live-migrating-qemu-kvm- > > virtual-machines/#live-migration for further details) > > OK, yeh the numbering is pretty arbitrary so it's not something I normally > think > about like that. > > > > > > > It was caused by commit 4c011c3 postcopy: Send whole huge pages > > > > > > > > I'm wondering that is it by design or is it a bug waiting for fix? > > > > > > This is the first report I've seen for it. How did you conclude > > > that > > > 4c011c3 caused it? While I can see it might have some effect on the > > > bandwidth management, I'm surprised it has this much effect. > > > > While digging into the bandwidth issue, Git bisect shows that this commit > > was > the first bad commit. > > OK. > > > > What size huge pages are you using - 2MB or 1GB? > > > > When I hit this issue I was using 1GB huge page size. > > I tested this issue with 2MB page size today On Gigabit LAN, Although > > the bandwidth control looks a little better than using 1GB, But not too > > much. > Please refer to the below test result. > > OK, I can certainly see why this might happen with 1GB huge pages; I need to > have a think about a fix. > > > > I can imagine we might have a problem that since we only do the > > > sleep between the hugepages, if we were using 1GB hugepages then > > > we'd see <big chunk of > > > data>[sleep]<big chunk of data>[sleep] which isn't as smooth as it used to > be. > > > > > > Can you give me some more details of your test? > > > > Live migration bandwidth management testing with 2MB hugepage size: > > sles12sp4_i440fx is a qemu/kvm guest with 6GB memory size. > > Note: the throughput value is approximating value. > > > > Terminal 1: > > virsh migrate-setspeed sles12sp4_i440fx $bandwidth && virsh migrate > > --live sles12sp4_i440fx qemu+tcp://5810f/system > > > > Terminal 2: > > virsh qemu-monitor-command sles12sp4_i440fx --hmp "info migrate" > > > > bandwidth=5 > > throughput: 160 mbps > > > > bandwidth=10 > > throughput: 167 mbps > > > > bandwidth=15 > > throughput: 168 mbps > > > > bandwidth=20 > > throughput: 168 mbps > > > > bandwidth=21 > > throughput: 336 mbps > > > > bandwidth=22 > > throughput: 336 mbps > > > > bandwidth=25 > > throughput: 335.87 mbps > > > > bandwidth=30 > > throughput: 335 mbps > > > > bandwidth=35 > > throughput: 335 mbps > > > > bandwidth=40 > > throughput: 335 mbps > > > > bandwidth=45 > > throughput: 504.00 mbps > > > > bandwidth=50 > > throughput: 500.00 mbps > > > > bandwidth=55 > > throughput: 500.00 mbps > > > > bandwidth=60 > > throughput: 500.00 mbps > > > > bandwidth=65 > > throughput: 650.00 mbps > > > > bandwidth=70 > > throughput: 660.00 mbps > > OK, so migrate-setspeed takes a bandwidth in MBytes/sec and I guess you're > throughput is in MBit/sec - so at the higher end it's about right, and at the > lower > end it's way off. > > Let me think about a fix for this. > > What are you using to measure throughput?
I use 'watch' command to observe the output of qemu hmp command 'info migrate', calculate the average value of throughput field during stage 2 of live migration. Thanks for taking time to dig into this issue, Lin
