Re: [RFC PATCH v2 0/7] x86/idle: add halt poll support

[Yang Zhang]

On 2017/8/29 22:56, Michael S. Tsirkin wrote:
> On Tue, Aug 29, 2017 at 11:46:34AM +0000, Yang Zhang wrote:
> > Some latency-intensive workload will see obviously performance
> > drop when running inside VM.
>
> But are we trading a lot of CPU for a bit of lower latency?
>
> > The main reason is that the overhead
> > is amplified when running inside VM. The most cost i have seen is
> > inside idle path.
> >
> > This patch introduces a new mechanism to poll for a while before
> > entering idle state. If schedule is needed during poll, then we
> > don't need to goes through the heavy overhead path.
>
> Isn't it the job of an idle driver to find the best way to
> halt the CPU?
>
> It looks like just by adding a cstate we can make it
> halt at higher latencies only. And at lower latencies,
> if it's doing a good job we can hopefully use mwait to
> stop the CPU.
>
> In fact I have been experimenting with exactly that.
> Some initial results are encouraging but I could use help
> with testing and especially tuning. If you can help
> pls let me know!

Quan, Can you help to test it and give result? Thanks.

--
Yang
Alibaba Cloud Computing