The Intel documentation recommends that spinlocks should use

loop:
	rep;nop;
	cmp $0,lock_var
	jne loop

ftp://download.intel.com/design/perftool/cbts/appnotes/sse2/w_spinlock.pdf

but the linux spinlock implementation uses

loop:
	cmp $0, lock_var
	rep; nop;
	jne loop.

Why?
According to the Intel documentation, rep nop is a predefined delay that
slows down the cpu to the speed of the memory bus. The linux
implementation will delay again _after_ the lock was released.

What about the attached patch? It also adds 'rep;nop' into the rw
spinlock implementation.

It boots with my Pentium III, but the cpu doesn't support 'rep nop'
(i.e. returns immediately)

--
	Manfred