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Date:   Mon, 5 Aug 2019 16:09:15 -0400
From:   Phil Auld <pauld@redhat.com>
To:     Julien Desfossez <jdesfossez@digitalocean.com>
Cc:     "Li, Aubrey" <aubrey.li@linux.intel.com>,
        Aaron Lu <aaron.lu@linux.alibaba.com>,
        Aubrey Li <aubrey.intel@gmail.com>,
        Subhra Mazumdar <subhra.mazumdar@oracle.com>,
        Vineeth Remanan Pillai <vpillai@digitalocean.com>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul Turner <pjt@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Greg Kerr <kerrnel@google.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3
Message-ID: <20190805200914.GD20173@pauld.bos.csb>
References: <635c01b0-d8f3-561b-5396-10c75ed03712@oracle.com>
 <20190613032246.GA17752@sinkpad>
 <CAERHkrsMFjjBpPZS7jDhzbob4PSmiPj83OfqEeiKgaDAU3ajOA@mail.gmail.com>
 <20190619183302.GA6775@sinkpad>
 <20190718100714.GA469@aaronlu>
 <CAERHkrtvLKxrpvfw04urAuougsYOWnNw4-H1vUDFx27Dvy0=Ww@mail.gmail.com>
 <20190725143003.GA992@aaronlu>
 <20190726152101.GA27884@sinkpad>
 <7dc86e3c-aa3f-905f-3745-01181a3b0dac@linux.intel.com>
 <20190802153715.GA18075@sinkpad>
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Hi,

On Fri, Aug 02, 2019 at 11:37:15AM -0400 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.
> 
> No tag
> ------
> Test                            Average     Stdev
> Alone                           1306.90     0.94
> nosmt                           649.95      1.44
> Aaron's full patchset:          828.15      32.45
> Aaron's first 2 patches:        832.12      36.53
> Aaron's 3rd patch alone:        864.21      3.68
> Tim's full patchset:            852.50      4.11
> Tim's full patchset + sched:    852.59      8.25
> 
> Sysbench mem untagged, sysbench cpu tagged
> ------------------------------------------
> Test                            Average     Stdev
> Alone                           1306.90     0.94
> nosmt                           649.95      1.44
> Aaron's full patchset:          586.06      1.77
> Aaron's first 2 patches:        630.08      47.30
> Aaron's 3rd patch alone:        1086.65     246.54
> Tim's full patchset:            852.50      4.11
> Tim's full patchset + sched:    390.49      15.76
> 
> Sysbench mem tagged, sysbench cpu untagged
> ------------------------------------------
> Test                            Average     Stdev
> Alone                           1306.90     0.94
> nosmt                           649.95      1.44
> Aaron's full patchset:          583.77      3.52
> Aaron's first 2 patches:        513.63      63.09
> Aaron's 3rd patch alone:        1171.23     3.35
> Tim's full patchset:            564.04      58.05
> Tim's full patchset + sched:    1026.16     49.43
> 
> Both sysbench tagged
> --------------------
> Test                            Average     Stdev
> Alone                           1306.90     0.94
> nosmt                           649.95      1.44
> Aaron's full patchset:          582.15      3.75
> Aaron's first 2 patches:        561.07      91.61
> Aaron's 3rd patch alone:        638.49      231.06
> Tim's full patchset:            679.43      70.07
> Tim's full patchset + sched:    664.34      210.14
> 

Sorry if I'm missing something obvious here but with only 2 processes 
of interest shouldn't one tagged and one untagged be about the same
as both tagged?  

In both cases the 2 sysbenches should not be running on the core at 
the same time. 

There will be times when oher non-related threads could share the core
with the untagged one. Is that enough to account for this difference?


Thanks,
Phil


> So in terms of fairness, Aaron's full patchset is the most consistent, but only
> Tim's patchset performs better than nosmt in some conditions.
> 
> Of course, this is one of the worst case scenario, as soon as we have
> multithreaded applications on overcommitted systems, core scheduling performs
> better than nosmt.
> 
> Thanks,
> 
> Julien

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