linux-kernel - Re: [PATCH AUTOSEL 4.20 163/304] sched/topology: Add lowest CPU asymmetry sched

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Message-ID: <20190128171939.GC3973@sasha-vm>
Date:   Mon, 28 Jan 2019 12:19:39 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>, adharmap@...eaurora.org,
        chris.redpath@....com, currojerez@...eup.net,
        dietmar.eggemann@....com, edubezval@...il.com,
        gregkh@...uxfoundation.org, javi.merino@...nel.org,
        joel@...lfernandes.org, juri.lelli@...hat.com,
        patrick.bellasi@....com, pkondeti@...eaurora.org,
        rjw@...ysocki.net, skannan@...eaurora.org, smuckle@...gle.com,
        srinivas.pandruvada@...ux.intel.com, thara.gopinath@...aro.org,
        tkjos@...gle.com, valentin.schneider@....com,
        vincent.guittot@...aro.org, viresh.kumar@...aro.org,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH AUTOSEL 4.20 163/304] sched/topology: Add lowest CPU
 asymmetry sched_domain level pointer

On Mon, Jan 28, 2019 at 04:14:17PM +0000, Quentin Perret wrote:
>Hi Sasha,
>
>On Monday 28 Jan 2019 at 10:41:20 (-0500), Sasha Levin wrote:
>> From: Quentin Perret <quentin.perret@....com>
>>
>> [ Upstream commit 011b27bb5d3139e8b5fe9ceff1fc7f6dc3145071 ]
>>
>> Add another member to the family of per-cpu sched_domain shortcut
>> pointers. This one, sd_asym_cpucapacity, points to the lowest level
>> at which the SD_ASYM_CPUCAPACITY flag is set. While at it, rename the
>> sd_asym shortcut to sd_asym_packing to avoid confusions.
>>
>> Generally speaking, the largest opportunity to save energy via
>> scheduling comes from a smarter exploitation of heterogeneous platforms
>> (i.e. big.LITTLE). Consequently, the sd_asym_cpucapacity shortcut will
>> be used at first as the lowest domain where Energy-Aware Scheduling
>> (EAS) should be applied. For example, it is possible to apply EAS within
>> a socket on a multi-socket system, as long as each socket has an
>> asymmetric topology. Energy-aware cross-sockets wake-up balancing will
>> only happen when the system is over-utilized, or this_cpu and prev_cpu
>> are in different sockets.
>
>Although I'm not really confident about the process for those AUTOSEL
>patches, I think this one alone won't help anybody without the other ~10
>EAS patches. And I assume you definitely don't want to mark those as
>stable, so I'm not sure if this one is a good candidate either.

I'll drop it then, thanks for the heads-up.

>On a side note, the best description I could find of AUTOSEL with a
>5 min Google search is this:  https://lwn.net/Articles/750057/
>Do you have any pointers to a doc where I can read up about AUTOSEL ?

For written material, this is based on Julia Lawall's work:
https://soarsmu.github.io/papers/icse12-patch.pdf .

We did a talk last year which is more recent than the paper:
https://www.youtube.com/watch?v=KWholDv6-Rw .

--
Thanks,
Sasha