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Date:   Tue, 8 Mar 2022 20:21:41 +1100
From:   Paul Bone <pbone@mozilla.com>
To:     linux-kernel@vger.kernel.org
Subject: Scheduling for heterogeneous computers
Message-ID: <20220308092141.GF748856@aluminium>
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Are there plans for power-aware scheduling on heterogeneous computers that
processes & threads can opt-in to?

Several mainstream devices now offer power-aware heterogeneous scheduling:

 * Lots of ARM (and therefore android) devices offer big.LITTLE cores.
 * Apple's M1 CPU has "gold" and "silver" cores.  The gold cores are faster
   and have more cache.  I think there are other microarchitectual
   differences.
 * Intel's Alder Lake CPUs have P and E cores.  I'm told that the E cores
   don't save power though since each core type still gets the same work
   done per Watt, it's just that the P cores are bigger and faster.
 * Multicore CPUs that offer frequency scaling could get some power savings
   by switching off turbo boost and similar features.  They wonThe work/watt
   improves at the cost of throughput & responsiveness.

I'm aware that Linux does some Energy Aware Scheduling
https://docs.kernel.org/scheduler/sched-energy.html, however what I'm
looking for is an API that processes (but ideally threads) can opt in-to
(and out-of (unlike nice)) to say that the work they're currently doing is
bulk work.  It needs to get done but it doesn't have a deadline and
therefore can be done on a smaller / more power efficient core.  The idea is
that the same work gets done eventually, but for a background task (eg
Garbage Collection) it can be done in a greener or more
battery-charge-extending way.

MacOS has added an API for this as:
    pthread_set_qos_class_self_np()
    https://developer.apple.com/documentation/apple-silicon/tuning-your-code-s-performance-for-apple-silicon?preferredLanguage=occ

Windows has:
    ThreadPowerThrottling
    https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-setthreadinformation

I'm not aware of anything for Linux and I've been unable to find anything.
Are there any plans to implement this?  

Cheers.