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

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Message-ID: <20200306183340.GC23145@pauld.bos.csb>
Date:   Fri, 6 Mar 2020 13:33:40 -0500
From:   Phil Auld <pauld@...hat.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Aaron Lu <aaron.lwe@...il.com>, Aubrey Li <aubrey.intel@...il.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 Fri, Mar 06, 2020 at 10:06:16AM -0800 Tim Chen wrote:
> 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.  
> 

cpu.shares is not quota. I think it will only get throttled if it has and 
exceeds quota.  Shares are supposed to be used to help weight contention
without providing a hard limit. 


Cheers,
Phil


> Tim
> 

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