On 14.02.2014 10:40, Joaquim Barrera wrote: > Hi all, > > As I am doing some tests with qemu, I realized that the way it does > 'migrate -i tcp:DEST:444' is not the same as 'libvirt migrate > --copy-storage-inc'. Basically qemu uses the same stream as RAM > migration and libvirt takes advantage of NBD transfer. > > With virsh migrate-setspeed I observed that one can only control the > transfer throughput of RAM, but not disk synchronization. At least this > is what I can see in bmon when doing a migration with incremental copy. > > The question is: Am I missing something or it is not implemented? > > Thank you guys! > I think this is actually a qemu bug. Libvirt passes the correct values: 2014-02-14 10:52:08.010+0000: 27701: debug : qemuMonitorIOWrite:504 : QEMU_MONITOR_IO_WRITE: mon=0x7f06cc00ea20 buf={"execute":"drive-mirror","arguments":{"device":"drive-virtio-disk0","target":"nbd:masina:49153:exportname=drive-virtio-disk0","speed":1048576,"sync":"full","mode":"existing"},"id":"libvirt-15"} ... 2014-02-14 10:53:51.169+0000: 27701: debug : qemuMonitorIOWrite:504 : QEMU_MONITOR_IO_WRITE: mon=0x7f06cc00ea20 buf={"execute":"migrate_set_speed","arguments":{"value":1048576},"id":"libvirt-221"} 2014-02-14 10:53:51.204+0000: 27701: debug : qemuMonitorIOWrite:504 : QEMU_MONITOR_IO_WRITE: mon=0x7f06cc00ea20 buf={"execute":"migrate","arguments":{"detach":true,"blk":false,"inc":false,"uri":"fd:migrate"},"id":"libvirt-223"} However I observe what you do - disk migration is not shaped, while internal state is.

> Thanks for raising this. > > I noticed that mirror_run() does not throttle the first loop where it > populates the dirty bitmap using bdrv_is_allocated_above(). This is on purpose. Does it causes a noticeable stall in the guest? > The main > copy loop does take the speed limit into account but perhaps that's > broken too. Yeah, it looks broken. Each iteration of the loop can write much more than sectors_per_chunk sectors, but here: if (s->common.speed) { delay_ns = ratelimit_calculate_delay(&s->limit, sectors_per_chunk); } else { delay_ns = 0; } the second argument is fixed. :/ Paolo

Il 28/02/2014 11:41, Joaquim Barrera ha scritto: >> > > Thanks for the answer. Something is still not clear to me. Are we in > front of a bug (that means, something that could be fixed) or is this > behaviour somehow expected for some reason? More and more tests I am > doing, I get allways the same throughput chart: unlimited bandwidth when > syncronizing the disk, and smooth bandwidth limit when migrating RAM. > > Joaquim Yes, it's a bug that we can fix.

Paolo