linux-kernel - Re: [RFC PATCH 0/2] PM / devfreq: Add delayed timer for polling

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Date:   Fri, 10 Jul 2020 17:12:33 +0200
From:   Willy Wolff <willy.mh.wolff.ml@...il.com>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Chanwoo Choi <cw00.choi@...sung.com>, k.konieczny@...sung.com,
        krzk@...nel.org, kgene@...nel.org, s.nawrocki@...sung.com,
        b.zolnierkie@...sung.com, chanwoo@...nel.org,
        myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 0/2] PM / devfreq: Add delayed timer for polling

Hi Lukasz,

On 2020-07-08-15-25-03, Lukasz Luba wrote:
> Hi Willy,
> 
> On 7/3/20 1:33 PM, Willy Wolff wrote:
> > Hi Chanwoo,
> > 
> > I think it doesn't help on the benchmark I suggested that is doing only memory
> > accesses. With both timer, I have the same timing.
> > 
> > To test the benchmark with these new patches about timer:
> > 
> > git clone https://github.com/wwilly/benchmark.git \
> >    && cd benchmark \
> >    && source env.sh \
> >    && ./bench_build.sh \
> >    && bash source/scripts/test_dvfs_mem_patched.sh
> > 
> > The benchmark is set by default to run for 1s, but you can increase this by
> > tweaking the script as:
> > 
> > taskset 8 ./bench_install/bin/microbe_cache 33554431 0 9722222 <TIME in sec> ${little_freq}
> > 
> > 
> > Also, as I reported the issue, would it be possible to add a
> > Reported-by: Willy Wolff <willy.mh.wolff.ml@...il.com> ?
> > Many thanks in advance.
> 
> Thank you for your good work and the benchmark. I hope you will continue
> to use it and report some issues. I am going to send a follow up patches
> for the DMC and I will add your 'Reported-by'. In the tests I can see
> the improvements, but it's worth to consult with you if I understand
> the new results correctly.
> 

Thanks for that. I will follow on the other patch thread discussion.

> I think there is still some area for improvements in the devfreq and you
> could find the interesting bits to contribute.

In fact, this benchmark is motivated about part of my PhD research that has just
been accepted at LCTES2020: "Performance Optimization on big.LITTLE Architectures:
A Memory-latency Aware Approach" at https://dl.acm.org/doi/10.1145/3372799.3394370

Basically, it's about snooping latency with "bad" CPU DVFS choice on big.LITTLE
systems or more generally SMP/AMP architecture. I'm cleaning up my code and will
propose patches as an RFC later. It introduces a new CPU DVFS governor to limit
snooping latency.

Cheers,
Willy

> 
> Regards,
> Lukasz
> 
> > 
> > 
> > Best Regards,
> > Willy
> >