linux-kernel - Re: [RFC][PATCH 00/13] percpu rwsem -v2

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Date:	Tue, 23 Jun 2015 16:34:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Wagner <daniel.wagner@...-carit.de>
Cc:	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, tj@...nel.org,
	mingo@...hat.com, linux-kernel@...r.kernel.org, der.herr@...r.at,
	dave@...olabs.net, riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org, jlayton@...chiereds.net
Subject: Re: [RFC][PATCH 00/13] percpu rwsem -v2

On Tue, Jun 23, 2015 at 11:35:24AM +0200, Daniel Wagner wrote:
> flock01
>                              mean   variance      sigma        max        min
>                     4.1.0    11.7075   816.3341    28.5716   125.6552     0.0021
>        4.1.0+percpu-rwsem    11.4614   760.1345    27.5705   132.5030     0.0026
>                       tip     6.8390   329.3037    18.1467    81.0373     0.0021
>          tip+percpu-rwsem    10.0870   546.7435    23.3825   106.2396     0.0026

> posix01
>                              mean   variance      sigma        max        min
>                     4.1.0   121.9020 27882.5260   166.9806   603.5509     0.0063
>        4.1.0+percpu-rwsem   185.3981 38474.3836   196.1489   580.6532     0.0073
>                       tip   129.2736 23752.7122   154.1191   474.0604     0.0063
>          tip+percpu-rwsem   142.6474 24732.1571   157.2646   468.7478     0.0072

Both these tests are incredibly unstable for me (as well as for you it
appears). Variance is through the roof on them.

I get runtimes like:

root@...-ex:/usr/local/src/lockperf# ./flock01 -n 240 -l 32 /tmp/a 
0.266157011
root@...-ex:/usr/local/src/lockperf# ./flock01 -n 240 -l 32 /tmp/a 
139.303399960

That's not really inspiring, if I use bigger loop counts it more or less
settles, but then the EX is unusable because it ends up running 3000
seconds per test.

In any case, on a smaller box (ivb-ep) I got the below results:

posix01
                                     mean   variance      sigma        max        min
data-4.1.0-02756-ge3d06bd         250.7032    40.4864     6.3629   263.7736   238.5192
data-4.1.0-02756-ge3d06bd-dirty   252.6847    35.8953     5.9913   270.1679   233.0215

Which looks better, but the difference is still well within the variance
and thus not significant.

Lemme continue playing with this for a bit more.
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