Re: [patch 04/15] Generic Mutex Subsystem, add-atomic-call-func-x86_64.patch
From: Nick Piggin
Date: Tue Dec 20 2005 - 21:11:28 EST
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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