linux-kernel - Re: [RFC PATCH v3 00/16] Core scheduling v3

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Date:   Mon, 5 Aug 2019 08:55:28 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Julien Desfossez <jdesfossez@...italocean.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     Aaron Lu <aaron.lu@...ux.alibaba.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        Vineeth Remanan Pillai <vpillai@...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>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.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 v3 00/16] Core scheduling v3

On 8/2/19 8:37 AM, Julien Desfossez wrote:
> We tested both Aaron's and Tim's patches and here are our results.
> 
> Test setup:
> - 2 1-thread sysbench, one running the cpu benchmark, the other one the
>   mem benchmark
> - both started at the same time
> - both are pinned on the same core (2 hardware threads)
> - 10 30-seconds runs
> - test script: https://paste.debian.net/plainh/834cf45c
> - only showing the CPU events/sec (higher is better)
> - tested 4 tag configurations:
>   - no tag
>   - sysbench mem untagged, sysbench cpu tagged
>   - sysbench mem tagged, sysbench cpu untagged
>   - both tagged with a different tag
> - "Alone" is the sysbench CPU running alone on the core, no tag
> - "nosmt" is both sysbench pinned on the same hardware thread, no tag
> - "Tim's full patchset + sched" is an experiment with Tim's patchset
>   combined with Aaron's "hack patch" to get rid of the remaining deep
>   idle cases
> - In all test cases, both tasks can run simultaneously (which was not
>   the case without those patches), but the standard deviation is a
>   pretty good indicator of the fairness/consistency.

Thanks for testing the patches and giving such detailed data.

I came to realize that for my scheme, the accumulated deficit of forced idle could be wiped
out in one execution of a task on the forced idle cpu, with the update of the min_vruntime,
even if the execution time could be far less than the accumulated deficit.
That's probably one reason my scheme didn't achieve fairness.

Tim