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List:       fuse-devel
Subject:    [fuse-devel] stat performance on multicore systems: measurements
From:       Stefan Westerfeld <stefan () space ! twc ! de>
Date:       2012-07-18 19:08:19
Message-ID: 20120718190818.GA17482 () space ! twc ! de
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   Hi!

As promised, I've created a test program that supports my theory that on
multicore systems, fuse performance for stat() and other calls could be
improved by scheduling the filesystem code that implements stat() and the
userspace process that calls stat() on the same cpu.

The first part of the test tries to figure out whether the userspace code
and the filesystem part of the code run on the same cpu or not. Note that
there is only one request at any single point in time, so the filesystem
is essentially single threaded.

The second part of the test then measures the stat() performance by calling=
 it
repeatedly; it computes how many stat() calls per second fuse can handle.

These two measurements are repeated with a cpu affinity schedule setting
that fixes the userspace code and the filesystem code on cpu 1. As I
expected, this cpu affinity setting makes things significantly faster.

Here are measurements for two multicore systems I have access to.

::::: AMD Phenom(tm) 9850 Quad-Core Processor
::::: Linux quadcorn 3.2.0-26-generic #41-Ubuntu SMP Thu Jun 14 17:49:24 UT=
C 2012 x86_64 x86_64 x86_64 GNU/Linux

stefan@quadcorn:~/src/sandbox/cputestfs$ runme.sh =

make: F=C3=BCr das Ziel =C2=BBall=C2=AB ist nichts zu tun.

#### without cpu affinity ####

same  cpu (%)     0.00
other cpu (%)   100.00
----------------------
stat calls/s  23025.13

#### with cpu affinity ####

same  cpu (%)   100.00
other cpu (%)     0.00
----------------------
stat calls/s  44334.30


::::: AMD Athlon(tm) 64 X2 Dual Core Processor 6400+
::::: Linux ubuntu 3.2.0-26-generic #41-Ubuntu SMP Thu Jun 14 17:49:24 UTC =
2012 x86_64 x86_64 x86_64 GNU/Linux

stefan@ubuntu:~/src/sandbox/cputestfs$ runme.sh                            =
                                                                           =
                                                                           =
                             =

make: F=C3=BCr das Ziel =C2=BBall=C2=AB ist nichts zu tun.                 =
                                                                           =
                                                                           =
                                            =

                                                                           =
                                                                           =
                                                                           =
                             =

#### without cpu affinity ####                                             =
                                                                           =
                                                                           =
                             =

                                                                           =
                                                                           =
                                                                           =
                             =

same  cpu (%)     3.10                                                     =
                                                                           =
                                                                           =
                             =

other cpu (%)    96.90                                                     =
                                                                           =
                                                                           =
                             =

----------------------                                                     =
                                                                           =
                                                                           =
                             =

stat calls/s  12164.21                                                     =
                                                                           =
                                                                           =
                             =

                                                                           =
                                                                           =
                                                                           =
                             =

#### with cpu affinity ####                                                =
                                                                           =
                                                                           =
                             =

                                                                           =
                                                                           =
                                                                           =
                             =

same  cpu (%)   100.00                                                     =
                                                                           =
                                                                           =
                             =

other cpu (%)     0.00
----------------------
stat calls/s  55163.82

My test code can be downloaded at: http://space.twc.de/~stefan/fuse/cputest=
fs.tar.bz2
It can be compiled & started by running the runme.sh script.

I hope that in the future, fuse can be modified so that it avoids scheduling
the filesystem code and the userspace code on different cpus. As the test
indicates, this will improve the performance of stat() and probably all oth=
er
filesystem calls.

   Cu... Stefan
-- =

Stefan Westerfeld, Hamburg/Germany, http://space.twc.de/~stefan

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