Re: REGRESSION: Performance regressions from switching anon_vma->lock to mutex

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On Wed, 2011-06-15 at 12:58 +0200, Peter Zijlstra wrote:
> On Wed, 2011-06-15 at 12:36 +0200, Peter Zijlstra wrote:
> > On Tue, 2011-06-14 at 17:29 -0700, Tim Chen wrote:
> > > MOSBENCH test suite.
> > 
> > Argh, I'm trying to get this thing to run, but its all snake poo..
> > 
> > /me takes up a heavy club and goes snake hunting, should make a pretty
> > hat or something.
> 
> Sweet, I've got meself a snake-skin hat!
> 
> The first thing that stood out when running it was:
> 
> 31694 root      20   0 26660 1460 1212 S 17.5  0.0   0:01.97 exim 
>     7 root      -2  19     0    0    0 S 12.7  0.0   0:06.14 rcuc0 
>    24 root      -2  19     0    0    0 S 11.7  0.0   0:04.15 rcuc3 
>    34 root      -2  19     0    0    0 S 11.7  0.0   0:04.10 rcuc5 
>    39 root      -2  19     0    0    0 S 11.7  0.0   0:06.38 rcuc6 
>    44 root      -2  19     0    0    0 S 11.7  0.0   0:04.53 rcuc7 
>    49 root      -2  19     0    0    0 S 11.7  0.0   0:04.11 rcuc8 
>    79 root      -2  19     0    0    0 S 11.7  0.0   0:03.91 rcuc14 
>    89 root      -2  19     0    0    0 S 11.7  0.0   0:03.90 rcuc16 
>   110 root      -2  19     0    0    0 S 11.7  0.0   0:03.90 rcuc20 
>   120 root      -2  19     0    0    0 S 11.7  0.0   0:03.82 rcuc22 
>    13 root      -2  19     0    0    0 S 10.7  0.0   0:04.37 rcuc1 
>    19 root      -2  19     0    0    0 S 10.7  0.0   0:04.19 rcuc2 
>    29 root      -2  19     0    0    0 S 10.7  0.0   0:04.12 rcuc4 
>    54 root      -2  19     0    0    0 S 10.7  0.0   0:04.11 rcuc9 
>    59 root      -2  19     0    0    0 S 10.7  0.0   0:04.40 rcuc10 
>    64 root      -2  19     0    0    0 R 10.7  0.0   0:04.17 rcuc11 
>    69 root      -2  19     0    0    0 R 10.7  0.0   0:04.23 rcuc12 
>    84 root      -2  19     0    0    0 S 10.7  0.0   0:03.90 rcuc15 
>    95 root      -2  19     0    0    0 S 10.7  0.0   0:03.99 rcuc17 
>   100 root      -2  19     0    0    0 S 10.7  0.0   0:03.88 rcuc18 
>   105 root      -2  19     0    0    0 S 10.7  0.0   0:04.14 rcuc19 
>   125 root      -2  19     0    0    0 S 10.7  0.0   0:03.79 rcuc23 
>    74 root      -2  19     0    0    0 S  9.7  0.0   0:04.33 rcuc13 
>   115 root      -2  19     0    0    0 R  9.7  0.0   0:03.82 rcuc21 
> 
> Which is an impressive amount of RCU usage..

FWIW, Alex Shi's patch:

http://lkml.kernel.org/r/1308029185.15392.147.camel@sli10-conroe

Improves the situation to:

 3745 root      20   0 26664 1460 1212 S 18.5  0.0   0:01.28 exim 
   39 root      -2  19     0    0    0 S  4.9  0.0   0:02.83 rcuc6 
  105 root      -2  19     0    0    0 S  4.9  0.0   0:02.79 rcuc19 
    7 root      -2  19     0    0    0 S  3.9  0.0   0:02.70 rcuc0 
   13 root      -2  19     0    0    0 S  3.9  0.0   0:02.54 rcuc1 
   19 root      -2  19     0    0    0 S  3.9  0.0   0:02.76 rcuc2 
   24 root      -2  19     0    0    0 S  3.9  0.0   0:02.75 rcuc3 
...

And throughput increases like:

-tip            260.092 messages/sec/core
-tip+sirq-rcu   271.078 messages/sec/core


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