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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.


Jean-Marc Saffroy - Research Engineer - Silicomp Research Institute

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