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List:       kvm
Subject:    RE: Virtio network performance problem
From:       "Adrian Schmitz" <aschmitz () lehighgas ! com>
Date:       2008-12-04 15:53:19
Message-ID: 3D753CDC7D3A054CADC4DC2DF4C9F66502027877 () LGC-MX01 ! corp ! lehighgas ! local
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> > On Wed, Dec 03, 2008 at 11:20:08AM -0800, Chris Wedgwood wrote:
> >
> > > TSC instability?  Is this an SMP guest?

Ok, I tried pinning the kvm process to two cores (0,2) on a single
socket, but that didn't seem to make any difference for my virtio
network performance. I also tried pinning the process to a single core,
which also didn't seem to have any effect.

Someone on IRC suggested that it sounded like a clocking issue, since
some of my ping times are negative. He suggested trying a different
clock source. I tried it with dynticks, rtc, and unix. None of them seem
better, although all of them seem "different" in terms of patterns in
the ping times. Sorry if this makes it a long post, but I don't know how
to describe it other than to paste an example (below). Not sure if this
indicates that it is clock-related or if it is meaningless.

In any event, I'm not sure where to go from here. Another suggestion
from IRC was that it was due to the age of my host kernel (2.6.18) and
the fact that it doesn't support high-res timers. If I can avoid
replacing the distro kernel, I'd like to, but I'll do what I have to, I
suppose.

With dynticks (these are all with -net user, as I had some trouble with
my tap interface last night while testing this. The results are roughly
the same as when I was using tap before, though):

Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=143ms TTL=255
Reply from 10.0.2.2: bytes=32 time=143ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=143ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-139ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-141ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-133ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=143ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255

With rtc:

Reply from 10.0.2.2: bytes=32 time=-224ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-223ms TTL=255
Reply from 10.0.2.2: bytes=32 time=4ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=225ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-223ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-224ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=225ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=225ms TTL=255
Reply from 10.0.2.2: bytes=32 time=225ms TTL=255

With unix:

Reply from 10.0.2.2: bytes=32 time=-191ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-191ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time<1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-190ms TTL=255
Reply from 10.0.2.2: bytes=32 time=-191ms TTL=255
Reply from 10.0.2.2: bytes=32 time=1ms TTL=255
Reply from 10.0.2.2: bytes=32 time=192ms TTL=255
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