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

From: Andi Kleen
Date: Mon Jul 10 2017 - 10:46:24 EST

On Mon, Jul 10, 2017 at 10:46:47AM +0200, Peter Zijlstra wrote:
> On Mon, Jul 10, 2017 at 09:38:30AM +0800, Aubrey Li wrote:
> > We measured 3%~5% improvemnt in disk IO workload, and 8%~20% improvement in
> > network workload.
> Argh, what a mess :/

The mess is really the current idle entry path. People keep putting more
and more slow stuff there, not realizing it's really a critical fast path.

> 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.