Subject: Re: [PATCH V2 6/6] vhost_net: correctly limit the max pending buffers

From: Jason Wang <[email-masked]>
Date: Mon, 02 Sep 2013 16:37:38 +0800

On 09/02/2013 02:30 PM, Jason Wang wrote:
> On 09/02/2013 01:56 PM, Michael S. Tsirkin wrote:
>> > On Fri, Aug 30, 2013 at 12:29:22PM +0800, Jason Wang wrote:
>>> >> As Michael point out, We used to limit the max pending DMAs to get better cache
>>> >> utilization. But it was not done correctly since it was one done when there's no
>>> >> new buffers submitted from guest. Guest can easily exceeds the limitation by
>>> >> keeping sending packets.
>>> >>
>>> >> So this patch moves the check into main loop. Tests shows about 5%-10%
>>> >> improvement on per cpu throughput for guest tx. But a 5% drop on per cpu
>>> >> transaction rate for a single session TCP_RR.
>> > Any explanation for the drop? single session TCP_RR is unlikely to
>> > exceed VHOST_MAX_PEND, correct?
> Unlikely to exceed. Recheck the result, looks like it was not stable
> enough. Will re-test and report.

Re-tested with more iterations, result shows no difference on TCP_RR
test and 5%-10% improvement on per cpu throughput for guest tx.

Will post V3 soon.