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SubjectRe: [patch 0/9] mutex subsystem, -V4
Date
Hi,

On Friday 23 December 2005 00:34, Christoph Hellwig wrote:

> c) semaphores are total overkill for 99% percent of the users. Remember
> this thing about optimizing for the common case?

Semaphores are not that different from mutexes.
What makes me suspicious is the large difference in the test results, that
either means something is wrong with the test or something is wrong with the
semaphores. From reading the discussion I still don't really know, why the
improvements to mutexes can't be applied to semaphores. I also haven't hardly
seen any discussion about why semaphores the way they are. Linus did suspect
there is a wakeup bug in the semaphore, but there was no conclusive followup
to that.
IMO there are still too many questions open, so I can understand Andrew. We
may only cover up the problem instead of fixing it. I understand that mutexes
have advantages, but if we compare them to semaphores it should be a fair
comparison, otherwise people start to think semaphores are something bad. The
majority of the discussion has been about microoptimisation, but on some
archs non-debug mutexes and semaphores may very well be the same thing.

bye, Roman

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