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    SubjectRe: [Q] Implementation of spin_lock on i386: why "rep;nop" ?
    On Mon, 17 Sep 2001, Dave Jones wrote:

    > On Mon, 17 Sep 2001, Jean-Marc Saffroy wrote:
    >
    > > What is the intent behind this "rep;nop" ? Does it really rely on an
    > > undocumented behaviour ?
    >
    > Its used to stop Pentium 4's from cooking themselves.
    > See the P4 manuals for more info.

    Ok, I found it: actually it is the PAUSE opcode in the P4 instruction set,
    and the doc for PAUSE mentions that it is equivalent to a NOP on older
    IA-32 processors.

    So no black magic here, except that "rep;nop" is a bit misleading, since
    the Intel docs for REP and NOP do not mention PAUSE...

    Thanks all for you help.


    Regards,

    --
    Jean-Marc Saffroy - Research Engineer - Silicomp Research Institute
    mailto:saffroy@ri.silicomp.fr

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