[haiku-bugs] Re: [Haiku] #5693: Implement pthread spinlocks (easy)
- From: "lucian" <trac@xxxxxxxxxxxx>
- Date: Sat, 17 Apr 2010 17:02:01 -0000
#5693: Implement pthread spinlocks (easy)
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Reporter: bonefish | Owner: nobody
Type: enhancement | Status: new
Priority: normal | Milestone: R1
Component: System/POSIX | Version: R1/Development
Keywords: | Blockedby:
Platform: All | Blocking:
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Comment(by lucian):
a) There's no much value, just a lower footprint (size/speed): I can skim
off a few call/ret instructions, and code it using better optimized asm.
b) The test is not really that superfluous.
Hammering the processor with instructions with LOCK prefixes (as in atomic
test and set) will block the memory lines for two cycles. In single
processor mode this will delay access to DMA, while in multiprocessor
setups this will delay all other processors too regardless of the
addresses used.
Ok, the _trylock one is not really that important as it is done only once,
but the one in the loop will lead to poorer performance.
See http://en.wikipedia.org/wiki/Test_and_Test-and-set
I'll run some tests to prove my claims.
c) I'll post a revised patch with LOCKED/UNLOCKED.
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Ticket URL: <http://dev.haiku-os.org/ticket/5693#comment:4>
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