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

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Date:   Thu, 12 Sep 2019 20:04:00 +0800
From:   Aaron Lu <aaron.lu@...ux.alibaba.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Julien Desfossez <jdesfossez@...italocean.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.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 Wed, Sep 11, 2019 at 09:19:02AM -0700, Tim Chen wrote:
> On 9/11/19 7:02 AM, Aaron Lu wrote:
> > Hi Tim & Julien,
> > 
> > On Fri, Sep 06, 2019 at 11:30:20AM -0700, Tim Chen wrote:
> >> On 8/7/19 10:10 AM, Tim Chen wrote:
> >>
> >>> 3) Load balancing between CPU cores
> >>> -----------------------------------
> >>> Say if one CPU core's sibling threads get forced idled
> >>> a lot as it has mostly incompatible tasks between the siblings,
> >>> moving the incompatible load to other cores and pulling
> >>> compatible load to the core could help CPU utilization.
> >>>
> >>> So just considering the load of a task is not enough during
> >>> load balancing, task compatibility also needs to be considered.
> >>> Peter has put in mechanisms to balance compatible tasks between
> >>> CPU thread siblings, but not across cores.
> >>>
> >>> Status:
> >>> I have not seen patches on this issue.  This issue could lead to
> >>> large variance in workload performance based on your luck
> >>> in placing the workload among the cores.
> >>>
> >>
> >> I've made an attempt in the following two patches to address
> >> the load balancing of mismatched load between the siblings.
> >>
> >> It is applied on top of Aaron's patches:
> >> - sched: Fix incorrect rq tagged as forced idle
> >> - wrapper for cfs_rq->min_vruntime
> >>   https://lore.kernel.org/lkml/20190725143127.GB992@aaronlu/
> >> - core vruntime comparison
> >>   https://lore.kernel.org/lkml/20190725143248.GC992@aaronlu/
> > 
> > So both of you are working on top of my 2 patches that deal with the
> > fairness issue, but I had the feeling Tim's alternative patches[1] are
> > simpler than mine and achieves the same result(after the force idle tag
> 
> I think Julien's result show that my patches did not do as well as
> your patches for fairness. Aubrey did some other testing with the same
> conclusion.  So I think keeping the forced idle time balanced is not
> enough for maintaining fairness.

Well, I have done following tests:
1 Julien's test script: https://paste.debian.net/plainh/834cf45c
2 start two tagged will-it-scale/page_fault1, see how each performs;
3 Aubrey's mysql test: https://github.com/aubreyli/coresched_bench.git

They all show your patchset performs equally well...And consider what
the patch does, I think they are really doing the same thing in
different ways.