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

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Message-ID: <20170713083649.febfflfl5hafkko5@hirez.programming.kicks-ass.net>
Date:   Thu, 13 Jul 2017 10:36:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        len.brown@...el.com, rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        arjan@...ux.intel.com, paulmck@...ux.vnet.ibm.com,
        yang.zhang.wz@...il.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On Wed, Jul 12, 2017 at 02:32:40PM -0700, Andi Kleen wrote:
> On Wed, Jul 12, 2017 at 10:34:10AM +0200, Peter Zijlstra wrote:
> > On Wed, Jul 12, 2017 at 12:15:08PM +0800, Li, Aubrey wrote:
> > > Okay, the difference is that Mike's patch uses a very simple algorithm to make the decision.
> > 
> > No, the difference is that we don't end up with duplication of a metric
> > ton of code.
> 
> What do you mean? There isn't much duplication from the fast path
> in Aubrey's patch kit.

A whole second idle path is one too many. We're not going to have
duplicate idle paths.

> It just moves some code around from the cpuidle governor to be generic,
> that accounts for the bulk of the changes. It's just moving however,
> not adding.

It wasn't at first glance evident it was a pure move because he does it
over a bunch of patches. Also, that code will not be moved to the
generic code, people are working on alternatives and very much rely on
this being a governor thing.

> > It uses the normal idle path, it just makes the NOHZ enter fail.
> 
> Which is only a small part of the problem.

Given the data so far provided it was by far the biggest problem. If you
want more things changed, you really have to give more data.