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    SubjectRe: sched_yield: delete sysctl_sched_compat_yield
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    On Fri, 2007-11-30 at 11:08 +0100, Ingo Molnar wrote:
    > * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
    >
    > > Haven't we been asking JVMs to use futexes or posix locking for years
    > > and years now? [...]
    >
    > i'm curious, with what JVM was it tested and where's the source so i can
    > fix their locking for them? Can the problem be reproduced with:
    >
    > http://download.fedora.redhat.com/pub/fedora/linux/development/source/SRPMS/java-1.7.0-icedtea-1.7.0.0-0.20.b23.snapshot.fc9.src.rpm
    I used BEA Jrockit to run volanoMark. Because of no Jrockit source codes, so
    I retested volanoMark by jre-1.7.0-icedtea.x86_64 java of Fedora Core 8 on my stoakley (8-core)
    machine with kernel 2.6.24-rc3.

    1) Jrockit: sched_compat_yield=0's result is less than 15% of sched_compat_yield=1's.
    2) jre-1.7.0-icedtea: sched_compat_yield=0's result is less than 89% of sched_compat_yield=1's.

    So JVM really has much impact on the regression.

    I checked the source codes of openjdk and found Thread.yield is implemented as native sched_yield.
    If java applications call Thread.yield, it just calls sched_yield. garbage collection and other JVM
    threads also calls Thread.yield. That's why 2 different JVM have different regression percentage.

    Although no source codes of volanoMark, I suspect it calls Thread.sched. volanoMark is a kind
    of chatroom benchmark. When a client sends out a message, server will send the message to all clients.
    I suspect the client calls Thread.yield after sending out a couple of messages.

    2 JVM all have regression if sched_compat_yield=0.

    I ran some testing, such like iozone/specjbb/tbench/dbench/sysbench, and didn't see regression.

    -yanmin



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