linux-kernel - Re: [PATCH V2 0/7] CPU cooling device new strategies

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Date:   Mon, 26 Mar 2018 22:30:46 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Eduardo Valentin <edubezval@...il.com>,
        kevin.wangtao@...aro.org, vincent.guittot@...aro.org,
        amit.kachhap@...il.com, linux-kernel@...r.kernel.org,
        javi.merino@...nel.org, rui.zhang@...el.com,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH V2 0/7] CPU cooling device new strategies

On Thu, Mar 08, 2018 at 12:03:52PM +0000, Daniel Thompson wrote:
> On Wed, Mar 07, 2018 at 07:57:17PM +0100, Daniel Lezcano wrote:
> > >> The preliminary benchmarks show the following changes:
> > >>
> > >> On the hikey6220, dhrystone shows a throughtput increase of 40% for an
> > >> increase of the latency of 16% while sysbench shows a latency increase
> > >> of 5%.
> > > 
> > > I don't follow these numbers. Throughput increase while injecting idle?
> > > compared to what? percentages of what? Please be more specific to better
> > > describer your work..
> > 
> > The dhrystone throughput is based on the virtual timer, when we are
> > running, it is at max opp, so the throughput increases. But regarding
> > the real time, it takes obviously more time to achieve as we are
> > artificially inserting idle cycles. With the cpufreq governor, we run at
> > a lower opp, so the throughput is less for dhrystone but it takes less
> > time to achieve.
> > 
> > Percentages are comparing cpufreq vs cpuidle cooling devices. I will
> > take care of presenting the results in a more clear way in the next version.
> 
> I think we should also note that the current hikey settings for cpufreq
> are very badly tuned for this platform. It has a single temp threshold
> and it jumps from max freq to min freq.
> 
> IIRC Leo's work on Hikey thermals correctly it would be much better if 
> it used the power-allocator thermal governor or if if copied some of 
> the Samsung 32-bit platform by configuring the step governor with a 
> graduated with a slightly lower threshold that moves two stops back in 
> the OPP table (which is still fairly high clock speed... but it
> thermally sustainable).

I think Daniel L. is working on this patch set with 'power-allocator'
governor, and the parameters 'sustainable-power = <3326>' and
'dynamic-power-coefficient = <311>' are profiling value on Hikey
platform.  Now we only consider dynamic power and skip static leakage
for 'power-allocator' governor.  And all these parameters are merged
into Linux mainline kernel.

Daniel L. could correct me if I misunderstand the testing conditions.

Thanks,
Leo Yan