Josh, Does this look like just more cpu usage due to caching? -Sam On Tue, Dec 18, 2012 at 12:37 AM, Jens Rehpöhler <jens.rehpoehler@xxxxxxxx> wrote: > Hi folks, > > i just received a mail of a customer. He reclaimed that the "ping > latency" of his VM rises, if he does a lot of IO > inside of the VM. I have done the same with a test VM. > > I could reproduce this behavior. If i disable the rbd cache the VM IO is > slower but the latency is ok. Even SSH und other > programs are affected .... so its not a problem of slow ICMP. > > Device Setting: > > virtio0: > rbd:9997/vm-1171-disk-1.rbd:rbd_cache=true:rbd_cache_size=16777216:rbd_cache_max_dirty=8388608:rbd_cache_target_dirty=4194304,cache=none > > normal ping: > > 64 bytes from 109.75.x.x: icmp_seq=38 ttl=56 time=29.2 ms > 64 bytes from 109.75.x.x: icmp_seq=39 ttl=56 time=20.8 ms > 64 bytes from 109.75.x.x: icmp_seq=40 ttl=56 time=22.4 ms > > with lots of IO: > > 64 bytes from 109.75.x.x: icmp_seq=87 ttl=56 time=28.1 ms > 64 bytes from 109.75.x.x: icmp_seq=88 ttl=56 time=665 ms > 64 bytes from 109.75.x.x: icmp_seq=89 ttl=56 time=226 ms > 64 bytes from 109.75.x.x: icmp_seq=90 ttl=56 time=179 ms > 64 bytes from 109.75.x.x: icmp_seq=91 ttl=56 time=140 ms > 64 bytes from 109.75.x.x: icmp_seq=92 ttl=56 time=25.6 ms > 64 bytes from 109.75.x.x: icmp_seq=93 ttl=56 time=568 ms > 64 bytes from 109.75.x.x: icmp_seq=94 ttl=56 time=405 ms > 64 bytes from 109.75.x.x: icmp_seq=95 ttl=56 time=223 ms > 64 bytes from 109.75.x.x: icmp_seq=96 ttl=56 time=24.5 ms > 64 bytes from 109.75.x.x: icmp_seq=97 ttl=56 time=321 ms > 64 bytes from 109.75.x.x: icmp_seq=98 ttl=56 time=391 ms > 64 bytes from 109.75.x.x: icmp_seq=99 ttl=56 time=4200 ms > 64 bytes from 109.75.x.x: icmp_seq=101 ttl=56 time=2194 ms > > But if i disable caching: > > virtio0: rbd:9997/vm-1171-disk-1.rbd:rbd_cache=false,cache=writeback > > with lots of IO: > > 64 bytes from 109.75.x.x: icmp_seq=62 ttl=56 time=22.1 ms > 64 bytes from 109.75.x.x: icmp_seq=63 ttl=56 time=26.5 ms > 64 bytes from 109.75.x.x: icmp_seq=64 ttl=56 time=30.7 ms > 64 bytes from 109.75.x.x: icmp_seq=65 ttl=56 time=24.8 ms > 64 bytes from 109.75.x.x: icmp_seq=66 ttl=56 time=21.9 ms > > Can someone please explain me this behavior ? Why is the latency of the > VM spiky if i enable rbd caching ? I've played around with the caching > parameters > but with caching enabled its always the same. > > KVM Version: 1.2.1 > Ceph Version: ceph version 0.48.2argonaut > (commit:3e02b2fad88c2a95d9c0c86878f10d1beb780bfe) > > Thanks a lot !! > > -- > mit freundlichen Grüssen > > Jens Rehpöhler > > ---------------------------------------------------------------------- > filoo GmbH > Moltkestr. 25a > 33330 Gütersloh > HRB4355 AG Gütersloh > > Geschäftsführer: S.Grewing | J.Rehpöhler | Dr. C.Kunz > Telefon: +49 5241 8673012 | Mobil: +49 151 54645798 > Hotline: +49 5241 8673026| Fax: +49 5241 8673020 > > Folgen Sie uns auf: > Twitter: http://twitter.com/filoogmbh > Facebook: http://facebook.com/filoogmbh > > -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
