Re: Network performance with small packets

On Wed, Feb 02, 2011 at 07:39:45AM -0800, Shirley Ma wrote:

On Wed, 2011-02-02 at 12:48 +0200, Michael S. Tsirkin wrote:

quoted

Yes, I think doing this in the host is much simpler,
just send an interrupt after there's a decent amount
of space in the queue.

Having said that the simple heuristic that I coded
might be a bit too simple.

quoted

From the debugging out what I have seen so far (a single small message

TCP_STEAM test), I think the right approach is to patch both guest and
vhost.

One problem is slowing down the guest helps here.
So there's a chance that just by adding complexity
in guest driver we get a small improvement :(

We can't rely on a patched guest anyway, so
I think it is best to test guest and host changes separately.

And I do agree something needs to be done in guest too,
for example when vqs share an interrupt, we
might invoke a callback when we see vq is not empty
even though it's not requested. Probably should
check interrupts enabled here?

The problem I have found is a regression for single  small
message TCP_STEAM test. Old kernel works well for TCP_STREAM, only new
kernel has problem.

Likely new kernel is faster :)

For Steven's problem, it's multiple stream TCP_RR issues, the old guest
doesn't perform well, so does new guest kernel. We tested reducing vhost
signaling patch before, it didn't help the performance at all.

Thanks
Shirley

Yes, it seems unrelated to tx interrupts.

-- 
MST