Re:[virtio-net][PATCH] Don't arm tx hrtimer with a constant 500us each transmit

On Tuesday 18 December 2007 16:30:08 Avi Kivity wrote:

Rusty Russell wrote:

quoted

    Yes, I pondered this when I wrote the code.  On the one hand, it's a
low-probability pathological corner case, on the other, your patch
reduces the number of timer reprograms in the normal case.

One thing that came up in our discussions is to let the host do the
timer processing instead of the guest.  When tx exit mitigation is
enabled, the guest bumps the queue pointer, but carefully refrains from
kicking the host.  The host polls the tx pointer using a timer, kicking
itself periodically; if polling yields no packets it disables tx exit
mitigation.  This saves the guest the bother of programming the timer,
which presumably requires an exit if the timer is the closest one to
expiration.

[btw, this can be implemented in virtqueue rather than virtio-net, no?]

Yes, the current patch is a hack (look at the hardcoded constant); wanted to 
see how much it helps, if any.

More sophisticated timer management would be a definite win... funny, I have a 
patch here which helps that....

Rusty.

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