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

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Message-ID: <fd482a4b-305b-5332-2f3e-f204018cc7b1@arm.com>
Date:   Mon, 13 Jul 2020 09:55:24 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Willy Wolff <willy.mh.wolff.ml@...il.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 Willy

On 7/10/20 4:12 PM, Willy Wolff wrote:
> 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
> 

Congrats and thank you for the link (I will read it).

> 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.

This is interesting, please add me on CC in the patch set.

Regards,
Lukasz