Nicolas Pitre wrote:
On Wed, 21 Dec 2005, Nick Piggin wrote:
Nicolas Pitre wrote:
On Tue, 20 Dec 2005, Nick Piggin wrote:
Considering that on UP, the arm should not need to disable interrupts
for this function (or has someone refuted Linus?), how about:
Kernel preemption.
preempt_disable() ?
Sure, and we're now more costly than the current implementation with irq
disabling.
Why? It is just a plain increment of a location that will almost certainly
be in cache. I can't see how it would be more than half the cost of the
irq implementation (based on looking at your measurements). How do you
figure?
Also, preempt_disable is a very frequent operation on preempt kernels so
if you have CONFIG_PREEMPT then you don't care about preempt_disable in
down() (and if you do then you are calling down too often).
If we go with simple mutexes that's because there is a gain, even a huge
one on ARM, especially for the fast uncontended case. If you guys
insist on making things so generic and rigid then there is no gain
anymore worth the bother.
I guess there is no bother for you, but maintaining code for 1 generic
platform versus two dozen architectures is a huge win for many.
--
SUSE Labs, Novell Inc.
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