On Wed, 2011-02-02 at 20:27 +0200, Michael S. Tsirkin wrote:

On Wed, Feb 02, 2011 at 10:11:51AM -0800, Shirley Ma wrote:

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On Wed, 2011-02-02 at 19:32 +0200, Michael S. Tsirkin wrote:

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OK, but this should have no effect with a vhost patch
which should ensure that we don't get an interrupt
until the queue is at least half empty.
Right?

There should be some coordination between guest and vhost.

What kind of coordination? With a patched vhost, and a full ring.
you should get an interrupt per 100 packets.
Is this what you see? And if yes, isn't the guest patch
doing nothing then?

vhost_signal won't be able send any TX interrupts to guest when guest TX
interrupt is disabled. Guest TX interrupt is only enabled when running
out of descriptors.

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We shouldn't
count the TX packets when netif queue is enabled since next guest TX
xmit will free any used buffers in vhost. We need to be careful here

in

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case we miss the interrupts when netif queue has stopped.

However we can't change old guest so we can test the patches

separately

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for guest only, vhost only, and the combination.

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Yes, it seems unrelated to tx interrupts. 

The issue is more likely related to latency.

Could be. Why do you think so?

Since I played with latency hack, I can see performance difference

for

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different latency.

Which hack was that? 

I tried to accumulate multiple guest to host notifications for TX xmits,
it did help multiple streams TCP_RR results; I also forced vhost
handle_tx to handle more packets; both hack seemed help.

Thanks
Shirley