That one is for tight loops. Spin locks are inlined, and PAUSE is used like:
#define spin_lock_string \
"\n1:\t" \
"lock ; decb %0\n\t" \
"js 2f\n" \
LOCK_SECTION_START("") \
"2:\t" \
"cmpb $0,%0\n\t" \
"rep;nop\n\t" \ <---
"jle 2b\n\t" \
"jmp 1b\n" \
LOCK_SECTION_END
Also take a look at arch/i386/kernel/semaphore.c for read/write_locks.
Jun
> -----Original Message-----
> From: Calin A. Culianu [mailto:calin@ajvar.org]
> Sent: Tuesday, December 03, 2002 7:42 AM
> To: Linux Kernel Mailing List
> Subject: SMP Pentium4 -- PAUSE Instruction
>
>
> I as wondering -- according to Intel's docs they recommend that on a P4
> processor to use the PAUSE instruction (aka rep followed by a nop) inside
> any spin loop (such as one used in SMP spinlock code) in order to both
> improve processor performance and reduce power consumption.
>
> Is this instruction being used in spin-wait loops? For some reason, I am
> having a hard time figuring out whether or not it is being used. There is
> a rep_nop() in processor.h.. but I can't determine if that is being called
> for spin lock lock/unlock code.
>
>
> -Calin
>
>
> -
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