linux-kernel - Re: [RFC PATCH v4 00/19] Core scheduling v4

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Date:   Fri, 6 Mar 2020 10:06:16 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Aaron Lu <aaron.lwe@...il.com>, Aubrey Li <aubrey.intel@...il.com>
Cc:     Phil Auld <pauld@...hat.com>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dario Faggioli <dfaggioli@...e.com>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v4 00/19] Core scheduling v4

On 3/5/20 6:41 PM, Aaron Lu wrote:

>>> So this appeared to me like a question of: is it desirable to protect/enhance
>>> high weight task performance in the presence of core scheduling?
>>
>> This sounds to me a policy VS mechanism question. Do you have any idea
>> how to spread high weight task among the cores with coresched enabled?
> 
> Yes I would like to get us on the same page of the expected behaviour
> before jumping to the implementation details. As for how to achieve
> that: I'm thinking about to make core wide load balanced and then high
> weight task shall spread on different cores. This isn't just about load
> balance, the initial task placement will also need to be considered of
> course if the high weight task only runs a small period.
> 

I am wondering why this is not happening:  

When the low weight task group has exceeded its cfs allocation during a cfs period, the task group
should be throttled.  In that case, the CPU cores that the low
weight task group occupies will become idle, and allow load balance from the
overloaded CPUs for the high weight task group to migrate over.  

Tim