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

Yang Zhang
2017-09-13T11:56:36Z

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