linux-kernel - Re: [PATCH] ARM: cpuidle: Support asymmetric idle definition

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Message-ID: <20170522133452.GC9325@leoy-ThinkPad-T440>
Date:   Mon, 22 May 2017 21:34:52 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>, rjw@...ysocki.net,
        lorenzo.pieralisi@....com,
        "open list:CPUIDLE DRIVERS" <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: cpuidle: Support asymmetric idle definition

Hi Sudeep,

On Mon, May 22, 2017 at 02:02:12PM +0100, Sudeep Holla wrote:

[...]

> >>>> On 19/05/17 17:45, Daniel Lezcano wrote:
> >>>>> Some hardware have clusters with different idle states. The current code does
> >>>>> not support this and fails as it expects all the idle states to be identical.
> >>>>>
> >>>>> Because of this, the Mediatek mtk8173 had to create the same idle state for a
> >>>>> big.Little system and now the Hisilicon 960 is facing the same situation.
> >>>>>
> >>>>
> >>>> While I agree the we don't support them today, it's better to benchmark
> >>>> and record/compare the gain we get with the support for cluster based
> >>>> idle states.
> >>>
> >>> Sorry, I don't get what you are talking about. What do you want to
> >>> benchmark ? Cluster idling ?
> >>>
> >>
> >> OK, I was not so clear. I had a brief chat with Lorenzo, we have few
> >> reason to have this support:
> >> 1. Different number of states between clusters
> >> 2. Different latencies(this is the one I was referring above, generally
> >>    we keep worst case timings here and wanted to see if any platform
> >>    measured improvements with different latencies in the idle states)
> > 
> > I don't see the point. Are you putting into question the big little design?
> >
> 
> Not exactly. Since they are generally worst case number, I wanted to
> check if someone saw real benefit with 2 different set of values.
> Anyways that's not important or blocking, just raised a point, so that
> we can stick some benchmarking results with this.

In case you are interesting for Hikey960 idle states, you could see
the two clustsers have different idle states:
http://termbin.com/d7ed

[...]

Thanks,
Leo Yan