Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

Peter Zijlstra
2017-07-13T18:28:44Z

On Thu, Jul 13, 2017 at 11:13:28PM +0800, Li, Aubrey wrote:
> On 2017/7/13 22:53, Peter Zijlstra wrote:

> > Fixing C-state selection by creating an alternative idle path sounds so
> > very wrong.
>
> This only happens on the arch which has multiple hardware idle cstates, like
> Intel's processor. As long as we want to support multiple cstates, we have to
> make a selection(with cost of timestamp update and computation). That's fine
> in the normal idle path, but if we want a fast idle switch, we can make a
> tradeoff to use a low-latency one directly, that's why I proposed a fast idle
> path, so that we don't need to mix fast idle condition judgement in both idle
> entry and idle exit path.

That doesn't make sense. If you can decide to pick a shallow C state in
any way, you can fix the general selection too.