Re: [patch 04/15] Generic Mutex Subsystem, add-atomic-call-func-x86_64.patch

[Nick Piggin <nickpiggin@yahoo.com.au>]

Nicolas Pitre wrote:
> On Tue, 20 Dec 2005, Linus Torvalds wrote:

> > IOW, why don't you just do
> >
> > 	ldr  lr,[%0]
> > 	subs lr, lr, %1
> > 	str  lr,[%0]
> > 	blmi failure
> >
> > as the _base_ timings, since that should be the common case. That's the 
> > drop-dead fastest UP case.
>
>
> The above is 5 cycles.  About the same as the preemption-safe swp-based 
> mutex implementation on non-Intel ARM.  It is broken wrt interrupts when 
> the swp is not.

How it is broken WRT interrupts? (sorry, I haven't had it explained to me
in words of two syllables or less)

--
SUSE Labs, Novell Inc.

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