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[Bug nptl/4209] New: Performance issue: NPTL semaphores work slower than linuxthreads semaphores


Some applications use semaphores for ensuring mutual exclusion, the purpose
mutexes are best suited for. By comparing the performance of such an application
with linuxthreads versus NPTL I discovered that under NPTL semaphores work
slower than under linuxthreads. This behavior occurs at least on ppc32 and i386.

The measurements I performed show that mutexes are about 30% faster under NPTL
than under linuxthreads, and that semaphores are about 70% slower:

$ uname -a
Linux pc-100 2.6.18.6 #8 Sun Feb 4 11:17:43 CET 2007 i686 athlon i386 GNU/Linux
$ /lib/libc.so.6
GNU C Library stable release version 2.5 (20061011), by Roland McGrath et al.
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Configured for i686-suse-linux.
Compiled by GNU CC version 4.1.2 20061115 (prerelease) (SUSE Linux).
Compiled on a Linux 2.6.18 system on 2006-11-26.
Available extensions:
        crypt add-on version 2.1 by Michael Glad and others
        GNU Libidn by Simon Josefsson
        GNU libio by Per Bothner
        NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
        NoVersion patch for broken glibc 2.0 binaries
        Native POSIX Threads Library by Ulrich Drepper et al
        BIND-8.2.3-T5B
Thread-local storage support included.
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.
$ /home/bart/glibc236/lib/libc.so.6
GNU C Library stable release version 2.3.6, by Roland McGrath et al.
Copyright (C) 2005 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.1.2 20061115 (prerelease) (SUSE Linux).
Compiled on a Linux >>2.6.18.6<< system on 2007-03-17.
Available extensions:
        GNU libio by Per Bothner
        crypt add-on version 2.1 by Michael Glad and others
        linuxthreads-0.10 by Xavier Leroy
        BIND-8.2.3-T5B
        libthread_db work sponsored by Alpha Processor Inc
        NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
Thread-local storage support included.
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.
$ ./perf
NPTL
mutex     Elapsed: 408611 us; per iteration: 40 ns.
semaphore Elapsed: 1901436 us; per iteration: 190 ns.
$ LD_LIBRARY_PATH=/home/bart/glibc236/lib: /home/bart/glibc236/lib/ld-linux.so.2
./glibc236-perf
linuxthreads
mutex     Elapsed: 538978 us; per iteration: 53 ns.
semaphore Elapsed: 1097891 us; per iteration: 109 ns.

-- 
           Summary: Performance issue: NPTL semaphores work slower than
                    linuxthreads semaphores
           Product: glibc
           Version: 2.4
            Status: NEW
          Severity: normal
          Priority: P2
         Component: nptl
        AssignedTo: drepper at redhat dot com
        ReportedBy: bart dot vanassche at gmail dot com
                CC: glibc-bugs at sources dot redhat dot com
 GCC build triplet: i686-suse-linux-gnu
  GCC host triplet: i686-suse-linux-gnu
GCC target triplet: i686-suse-linux-gnu


http://sourceware.org/bugzilla/show_bug.cgi?id=4209

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