Re: [PATCH 0/4] [RFC] virtio-net: Improve small packet performance

On Thu, May 05, 2011 at 03:13:43PM +0530, Krishna Kumar2 wrote:

"Michael S. Tsirkin" [off-list ref] wrote on 05/05/2011 02:34:39 PM:

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It shows that 2.9% of the time, the 1 jiffy was not enough
to free up space in the txq.

How common is it to free up space in *less than* 1 jiffy?

True,

Sorry, which statement do you say is true? That interrupt
after less than 1 jiffy is common?

but the point is that the space freed is just
enough for 43 entries, keeping it lower means a flood
of (psuedo) stop's and restart's.

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That could also mean that we
had set xmit_restart just before jiffies changed. But the
average free capacity when we *resumed* xmits is:
Sum of slots / (Good + Bad) = 43.

So the delay of 1 jiffy helped the host clean up, on average,
just 43 entries, which is 16% of total entries. This is
intended to show that the guest is not sitting idle waiting
for the jiffy to expire.

OK, nice, this is exactly what my patchset is trying
to do, without playing with timers: tell the host
to interrupt us after 3/4 of the ring is free.
Why 3/4 and not all of the ring? My hope is we can
get some parallelism with the host this way.
Why 3/4 and not 7/8? No idea :)

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I can post it, mind testing this?

Sure.

Just posted. Would appreciate feedback.

Do I need to apply all the patches and simply test?

Thanks,

- KK

Exactly. You can also try to tune the threshold
for interrupts as well.

Could you send me (privately) the entire virtio-net/vhost
patch in a single file? It will help me quite a bit :)
Either attachment or inline is fine.

thanks,

- KK

Better yet, here they are in git:

git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git vhost-net-next-event-idx-v1
git://git.kernel.org/pub/scm/linux/kernel/git/mst/qemu-kvm.git virtio-net-event-idx-v1


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