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

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Message-ID: <20200227020432.GA628749@ziqianlu-desktop.localdomain>
Date:   Thu, 27 Feb 2020 10:04:32 +0800
From:   Aaron Lu <aaron.lwe@...il.com>
To:     Vineeth Remanan Pillai <vpillai@...italocean.com>
Cc:     Aubrey Li <aubrey.intel@...il.com>,
        Tim Chen <tim.c.chen@...ux.intel.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>, 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 v4 00/19] Core scheduling v4

On Tue, Feb 25, 2020 at 03:51:37PM -0500, Vineeth Remanan Pillai wrote:
> On a 2sockets/16cores/32threads VM, I grouped 8 sysbench(cpu mode)
> > threads into one cgroup(cgA) and another 16 sysbench(cpu mode) threads
> > into another cgroup(cgB). cgA and cgB's cpusets are set to the same
> > socket's 8 cores/16 CPUs and cgA's cpu.shares is set to 10240 while cgB's
> > cpu.shares is set to 2(so consider cgB as noise workload and cgA as
> > the real workload).
> >
> > I had expected cgA to occupy 8 cpus(with each cpu on a different core)
> 
> The expected behaviour could also be that 8 processes share 4 cores and
> 8 hw threads right? This is what we are seeing mostly

I expect the 8 cgA tasks to spread on each core, instead of occupying
4 cores/8 hw threads. If they stay on 4 cores/8 hw threads, than on the
core level, these cores' load would be much higher than other cores
which are running cgB's tasks, this doesn't look right to me.

I think the end result should be: each core has two tasks queued, one
cgA task and one cgB task(to maintain load balance on the core level).
The two tasks are queued on different hw thread, with cgA's task runs
most of the time on one thread and cgB's task being forced idle most
of the time on the other thread.