linux-kernel - Re: Hackbench pipes regression bisected to PSI

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Message-ID: <20181126232926.GS23260@techsingularity.net>
Date:   Mon, 26 Nov 2018 23:29:26 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: Hackbench pipes regression bisected to PSI

On Mon, Nov 26, 2018 at 12:32:18PM -0500, Johannes Weiner wrote:
> > 
> > Bit late to notice but this switch should be in
> > Documentation/admin-guide/kernel-parameters.txt. If you really want to
> > match the automatic numa balancing switch then it also should be
> > psi=[enable|disable] instead of psi_enable=[1|0]
> 
> Done and done, thanks. Updated patch:
> 

The following is a comparision using CONFIG_PSI=n as a baseline against
your patch and a vanilla kernel

                         4.20.0-rc4             4.20.0-rc4             4.20.0-rc4
                kconfigdisable-v1r1                vanilla        psidisable-v1r1
Amean     1       1.3100 (   0.00%)      1.3923 (  -6.28%)      1.3427 (  -2.49%)
Amean     3       3.8860 (   0.00%)      4.1230 *  -6.10%*      3.8860 (  -0.00%)
Amean     5       6.8847 (   0.00%)      8.0390 * -16.77%*      6.7727 (   1.63%)
Amean     7       9.9310 (   0.00%)     10.8367 *  -9.12%*      9.9910 (  -0.60%)
Amean     12     16.6577 (   0.00%)     18.2363 *  -9.48%*     17.1083 (  -2.71%)
Amean     18     26.5133 (   0.00%)     27.8833 *  -5.17%*     25.7663 (   2.82%)
Amean     24     34.3003 (   0.00%)     34.6830 (  -1.12%)     32.0450 (   6.58%)
Amean     30     40.0063 (   0.00%)     40.5800 (  -1.43%)     41.5087 (  -3.76%)
Amean     32     40.1407 (   0.00%)     41.2273 (  -2.71%)     39.9417 (   0.50%)

It's showing that the vanilla kernel takes a hit (as the bisection
indicated it would) and that disabling PSI by default is reasonably
close in terms of performance for this particular workload on this
particular machine so;

Tested-by: Mel Gorman <mgorman@...hsingularity.net>

Thanks!

-- 
Mel Gorman
SUSE Labs