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

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Message-ID: <20181203161633.GK2509588@devbig004.ftw2.facebook.com>
Date:   Mon, 3 Dec 2018 08:16:33 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     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,
        mhocko@...nel.org, mike.kravetz@...cle.com,
        Pavel.Tatashin@...rosoft.com, prasad.singamsetty@...cle.com,
        rdunlap@...radead.org, steven.sistare@...cle.com,
        tim.c.chen@...el.com, vbabka@...e.cz, peterz@...radead.org,
        dhaval.giani@...cle.com
Subject: Re: [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work

Hello,

On Fri, Nov 30, 2018 at 04:13:07PM -0800, Daniel Jordan wrote:
> On Fri, Nov 30, 2018 at 11:18:19AM -0800, Tejun Heo wrote:
> > Hello,
> > 
> > On Mon, Nov 05, 2018 at 11:55:45AM -0500, 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.
> > 
> > Have you tested what kind of impact this has on bandwidth of a system
> > in addition to latency?  The thing is while this would make a better
> > use of a system which has idle capacity, it does so by doing more
> > total work.  It'd be really interesting to see how this affects
> > bandwidth of a system too.
> 
> I guess you mean something like comparing aggregate CPU time across threads to
> the base single thread time for some job or set of jobs?  Then no, I haven't
> measured that, but I can for next time.

Yeah, I'm primarily curious how expensive this is on an already loaded
system, so sth like loading up the system with a workload which can
saturate the system and comparing the bw impacts of serial and
parallel page clearings at the same frequency.

Thanks.

-- 
tejun