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Subject: Re: [RFC v5 4/6] sched/fair: Tune task wake-up logic to pack small
 background tasks on fewer cores
To:     Parth Shah <parth@linux.ibm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        "open list:THERMAL" <linux-pm@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Patrick Bellasi <patrick.bellasi@matbug.net>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Pavel Machek <pavel@ucw.cz>,
        Doug Smythies <dsmythies@telus.net>,
        Quentin Perret <qperret@qperret.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>
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 <80bb34ec-6358-f4dc-d20d-cde6c9d7e197@linux.ibm.com>
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From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <6a620fc4-daf9-dd02-7a81-3d9364bfe162@arm.com>
Date:   Thu, 10 Oct 2019 16:53:12 +0200
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On 09/10/2019 19:02, Parth Shah wrote:
> 
> 
> On 10/9/19 7:56 PM, Dietmar Eggemann wrote:
>> On 09/10/2019 10:57, Parth Shah wrote:
>>
>> [...]
>>
>>>> On 07/10/2019 18:53, Parth Shah wrote:
>>>>>
>>>>>
>>>>> On 10/7/19 5:49 PM, Vincent Guittot wrote:
>>>>>> On Mon, 7 Oct 2019 at 10:31, Parth Shah <parth@linux.ibm.com> wrote:

[...]

> ok. so does that mean TurboSched can still do some good in such systems as
> well ?
> I mean save energy even when rd->overutilized==1 by not waking user
> classified bg tasks on idle core.

I wouldn't say it is impossible but how likely would it be?

The Android runtime already classifies its tasks into groups such as
background, foreground, top-app, etc. It uses existing infrastructure
like cpusets, taskgroups, util_clamp (or its out-of-tree predecessor
schedtune) as well as EAS/Energy Model on asymmetric CPU capacity
systems to map them (differently) onto the CPU topology to achieve the
best possible performance/energy consumption trade-off.

Moreover, Google and Arm are keen getting the concept of 'latency nice'
upstream so we can map Android Common Kernel's 'prefer idle' feature
into the mainline energy-aware wu path.

So I'm afraid the question whether TurboSched could make sense on an
Android system can only be answered by people responsible for future
Android runtime architecture.