Messages in this thread | | | Date | Thu, 29 Dec 2005 20:01:38 +1100 | From | Nick Piggin <> | Subject | Re: [patch 1/3] mutex subsystem: trylock |
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Ingo Molnar wrote: > * Nicolas Pitre <nico@cam.org> wrote:
>>+ "1: ldrex %0, [%3] \n" >>+ "subs %1, %0, #1 \n" >>+ "strexeq %2, %1, [%3] \n" >>+ "movlt %0, #0 \n" >>+ "cmpeq %2, #0 \n" >>+ "bgt 1b \n" > > > so we are back to what is in essence a cmpxchg implementation? >
FWIW, I still think we should go for an open-coded "cmpxchg" variant for UP that disables preempt, and an atomic_cmpxchg variant for SMP.
- good generic implementations - the UP version is faster than atomic_xchg for non preempt on ARM - if you really are counting cycles, you'd probably have preempt off - if you've got preempt on then the preempt_ operations in semaphores would be the least of your worries (how about spinlocks?)
Rather than straight out introducing lots of ugliness and complexity for something that actually slows down the speed critical !preempt case (but is unlikely to be measurable either way).
-- SUSE Labs, Novell Inc.
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