linux-kernel - Re: [PATCH V2 0/3] Introduce Thermal Pressure

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Date:   Wed, 17 Apr 2019 07:55:14 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, rui.zhang@...el.com,
        linux-kernel@...r.kernel.org, amit.kachhap@...il.com,
        viresh.kumar@...aro.org, javi.merino@...nel.org,
        edubezval@...il.com, daniel.lezcano@...aro.org,
        vincent.guittot@...aro.org, nicolas.dechesne@...aro.org,
        bjorn.andersson@...aro.org, dietmar.eggemann@....com
Subject: Re: [PATCH V2 0/3] Introduce Thermal Pressure


* Ingo Molnar <mingo@...nel.org> wrote:

> * Thara Gopinath <thara.gopinath@...aro.org> wrote:
> 
> > The test results below shows 3-5% improvement in performance when
> > using the third solution compared to the default system today where
> > scheduler is unware of cpu capacity limitations due to thermal events.
> 
> The numbers look very promising!
> 
> I've rearranged the results to make the performance properties of the 
> various approaches and parameters easier to see:
> 
>                                          (seconds, lower is better)
> 
> 			                 Hackbench   Aobench   Dhrystone
>                                          =========   =======   =========
> Vanilla kernel (No Thermal Pressure)         10.21    141.58        1.14
> Instantaneous thermal pressure               10.16    141.63        1.15
> Thermal Pressure Averaging:
>       - PELT fmwk                             9.88    134.48        1.19
>       - non-PELT Algo. Decay : 500 ms         9.94    133.62        1.09
>       - non-PELT Algo. Decay : 250 ms         7.52    137.22        1.012
>       - non-PELT Algo. Decay : 125 ms         9.87    137.55        1.12

So what I forgot to say is that IMO your results show robust improvements 
over the vanilla kernel of around 5%, with a relatively straightforward 
thermal pressure metric. So I suspect we could do something like this, if 
there was a bit more measurements done to get the best decay period 
established - the 125-250-500 msecs results seem a bit coarse and not 
entirely unambiguous.

In terms of stddev: the perf stat --pre hook could be used to add a dummy 
benchmark run, to heat up the test system, to get more reliable, less 
noisy numbers?

BTW., that big improvement in hackbench results to 7.52 at 250 msecs, is 
that real, or a fluke perhaps?

Thanks,

	Ingo