Is it possible to make -lpthread program to use 100% CPU?

From: Alexandre (Alex.Kovalenko_at_verizon.net)
Date: 04/29/04

  • Next message: Ivan Voras: "Re: Is it possible to make -lpthread program to use 100% CPU?" 
    Date: Thu, 29 Apr 2004 11:13:55 -0400
To: current@freebsd.org

    Good people,

    I apologize for possible off-topic, but since we have new default threading
    library in -current, I thought it proper to ask this question here.

    Another (hopefully unnecessary) disclaimer -- I am not looking forward to
    sparking controversy over comparative merits of libthr and new
    libpthread (libkse?).

    I just would like a pointer to the tunable or a pthread_attribute value which
    would allow me to use my hardware at 100% with new default threading library.

    The reason for the question is dramatic difference in performance
    between libthr and libpthread on my application. Application in
    question performs heavy duty computation on relatively small amount of data.
    For those, familiar with Adobe PDF, it comutes O-Value, given user password.
    Computation involves RC4 and MD5 and uses OpenSSL library. Since computation
    is performed on the range of passwords, range could be arbitrarily broken
    into smaller subranges and fed to independent processing threads.

    Number of per/second computations for program built with -lpthread seems to
    be 20-30% lower comparing to the same program built with -lthr. Fittingly,
    'top' reports 20-30% lower CPU utilization (basically starting with 4
    threads it reports solid 100% for libthr and 75-80% with libpthread). At 32
    threads with libpthread CPU utilization is somewhere around 90-95% and
    performance is about 25%.

    Hardware in question is dual 2.4GHz Xeon with HyperThreading enabled.

    Kernel is built with no WITNESS or INVARIANTS.

    There is seem to be no difference between SCHED_4BSD and SCHED_ULE.

    Threads were created with SCOPE_SYSTEM for libthr and with both _SYSTEM
    and _PROCESS for libpthread. With SCOPE_SYSTEM, libpthread starts catching
    up to its own SCOPE_PROCESS performance at much higher number of threads (16+).

    Any suggestions would be appreciated.

    Alternatively, if there is a need to test a patch or time a program
    in this environment, it could easily be accomplished -- it is a non-
    production box. 

    -- 
Alexandre "Sunny" Kovalenko.
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  • Next message: Ivan Voras: "Re: Is it possible to make -lpthread program to use 100% CPU?"

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