linux-kernel - Re: [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work

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Message-ID: <20181106012955.br5swua3ykvolyjq@ca-dmjordan1.us.oracle.com>
Date:   Mon, 5 Nov 2018 17:29:55 -0800
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>, linux-mm@...ck.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        aarcange@...hat.com, aaron.lu@...el.com, akpm@...ux-foundation.org,
        alex.williamson@...hat.com, bsd@...hat.com,
        darrick.wong@...cle.com, dave.hansen@...ux.intel.com,
        jgg@...lanox.com, jwadams@...gle.com, jiangshanlai@...il.com,
        mike.kravetz@...cle.com, Pavel.Tatashin@...rosoft.com,
        prasad.singamsetty@...cle.com, rdunlap@...radead.org,
        steven.sistare@...cle.com, tim.c.chen@...el.com, tj@...nel.org,
        vbabka@...e.cz
Subject: Re: [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work

On Mon, Nov 05, 2018 at 06:29:31PM +0100, Michal Hocko wrote:
> On Mon 05-11-18 11:55:45, Daniel Jordan wrote:
> > Michal, you mentioned that ktask should be sensitive to CPU utilization[1].
> > ktask threads now run at the lowest priority on the system to avoid disturbing
> > busy CPUs (more details in patches 4 and 5).  Does this address your concern?
> > The plan to address your other comments is explained below.
> 
> I have only glanced through the documentation patch and it looks like it
> will be much less disruptive than the previous attempts. Now the obvious
> question is how does this behave on a moderately or even busy system
> when you compare that to a single threaded execution. Some numbers about
> best/worst case execution would be really helpful.

Patches 4 and 5 have some numbers where a ktask and non-ktask workload compete
against each other.  Those show either 8 ktask threads on 8 CPUs (worst case) or no ktask threads (best case).

By single threaded execution, I guess you mean 1 ktask thread.  I'll run the
experiments that way too and post the numbers.

> I will look closer later.

Great!  Thanks for your comment.

Daniel