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

Peter Zijlstra
2017-07-10T16:42:19Z

On Mon, Jul 10, 2017 at 07:46:09AM -0700, Andi Kleen wrote:
> > So how much of the gain is simply due to skipping NOHZ? Mike used to
> > carry a patch that would throttle NOHZ. And that is a _far_ smaller and
> > simpler patch to do.
>
> Have you ever looked at a ftrace or PT trace of the idle entry?
>
> There's just too much stuff going on there. NOHZ is just the tip
> of the iceberg.

I have, and last time I did the actual poking at the LAPIC (to make NOHZ
happen) was by far the slowest thing happening.

Data to indicate what hurts how much would be a very good addition to
the Changelogs. Clearly you have some, you really should have shared.