linux-kernel - Re: [RFC v4 0/8] TurboSched: A scheduler for sustaining Turbo Frequencies for longer durations

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Message-ID: <20190728133102.GD8718@xo-6d-61-c0.localdomain>
Date:   Sun, 28 Jul 2019 15:31:02 +0200
From:   Pavel Machek <pavel@....cz>
To:     Parth Shah <parth@...ux.ibm.com>
Cc:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        patrick.bellasi@....com, dietmar.eggemann@....com,
        daniel.lezcano@...aro.org, subhra.mazumdar@...cle.com
Subject: Re: [RFC v4 0/8] TurboSched: A scheduler for sustaining Turbo
 Frequencies for longer durations

Hi!

> Abstract
> ========
> 
> The modern servers allows multiple cores to run at range of frequencies
> higher than rated range of frequencies. But the power budget of the system
> inhibits sustaining these higher frequencies for longer durations.

Thermal budget?

Should this go to documentation somewhere?

> Current CFS algorithm in kernel scheduler is performance oriented and hence
> tries to assign any idle CPU first for the waking up of new tasks. This
> policy is perfect for major categories of the workload, but for jitter
> tasks, one can save energy by packing them onto the active cores and allow
> those cores to run at higher frequencies.
> 
> These patch-set tunes the task wake up logic in scheduler to pack
> exclusively classified jitter tasks onto busy cores. The work involves the
> jitter tasks classifications by using syscall based mechanisms.
> 
> In brief, if we can pack jitter tasks on busy cores then we can save power
> by keeping other cores idle and allow busier cores to run at turbo
> frequencies, patch-set tries to meet this solution in simplest manner.
> Though, there are some challenges in implementing it(like smt_capacity,

Space before (.

> These numbers are w.r.t. `turbo_bench.c` multi-threaded test benchmark
> which can create two kinds of tasks: CPU bound (High Utilization) and
> Jitters (Low Utilization). N in X-axis represents N-CPU bound and N-Jitter
> tasks spawned.

Ok, so you have description how it causes 13% improvements. Do you also have metrics how
it harms performance.. how much delay is added to unimportant tasks etc...?

Thanks,
										Pavel