Messages in this thread | | | Date | Wed, 27 Jun 2007 16:20:16 +1000 | From | Nick Piggin <> | Subject | Re: [BUG] long freezes on thinkpad t60 |
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Linus Torvalds wrote: > > On Wed, 27 Jun 2007, Nick Piggin wrote: > >>I don't know why my unlock sequence should be that much slower? Unlocked >>mov vs unlocked add? Definitely in dumb micro-benchmark testing it wasn't >>twice as slow (IIRC). > > > Oh, that releasing "add" can be unlocked, and only the holder of the lock > ever touches that field?
Right.
> I must not have looked closely enough. In that case, I withdraw that > objection, and the sequence-number-based spinlock sounds like a perfectly > fine one. > > Yes, the add will be slightly slower than the plain byte move, and the > locked xadd will be slightly slower than a regular locked add, but > compared to the serialization cost, that should be small. For some reason > I thought you needed a locked instruction for the unlock too. > > So try it with just a byte counter, and test some stupid micro-benchmark > on both a P4 and a Core 2 Duo, and if it's in the noise, maybe we can make > it the normal spinlock sequence just because it isn't noticeably slower. > > In fact, I think a "incb <mem>" instruction is even a byte shorter than > "movb $1,mem", and with "unlock" being inlined, that could actually be a > slight _win_.
OK, I'll try running some tests and get back to you on it.
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