linux-kernel - Re: [mm] 755d6edc1a: will-it-scale.per_process

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Date:   Tue, 6 Aug 2019 13:11:09 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     kernel test robot <oliver.sang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Miguel de Dios <migueldedios@...gle.com>,
        Wei Wang <wvw@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>, lkp@...org
Subject: Re: [mm]  755d6edc1a:  will-it-scale.per_process_ops -4.1% regression

On Tue 06-08-19 20:00:24, Minchan Kim wrote:
> On Tue, Aug 06, 2019 at 10:04:15AM +0200, Michal Hocko wrote:
> > On Tue 06-08-19 15:05:47, kernel test robot wrote:
> > > Greeting,
> > > 
> > > FYI, we noticed a -4.1% regression of will-it-scale.per_process_ops due to commit:
> > 
> > I have to confess I cannot make much sense from numbers because they
> > seem to be too volatile and the main contributor doesn't stand up for
> > me. Anyway, regressions on microbenchmarks like this are not all that
> > surprising when a locking is slightly changed and the critical section
> > made shorter. I have seen that in the past already.
> 
> I guess if it's multi process workload. The patch will give more chance
> to be scheduled out so TLB miss ratio would be bigger than old.
> I see it's natural trade-off for latency vs. performance so only thing
> I could think is just increase threshold from 32 to 64 or 128?

This still feels like a magic number tunning, doesn't it?

-- 
Michal Hocko
SUSE Labs