Re: [patch] speed up / fix the new generic semaphore code (fix AIM740% regression with 2.6.26-rc1)

[Linus Torvalds]

On Thu, 8 May 2008, Ingo Molnar wrote:
> 
> Peter pointed it out that because sem->count is u32, the <= 0 is in fact 
> a "== 0" condition - the patch below does that. As expected gcc figured 
> out the same thing too so the resulting code output did not change. (so 
> this is just a cleanup)

Why don't we just make it do the same thing that the x86 semaphores used 
to do: make it signed, and decrement unconditionally. And callt eh 
slow-path if it became negative.

IOW, make the fast-path be

	spin_lock_irqsave(&sem->lock, flags);
	if (--sem->count < 0)
		__down();
	spin_unlock_irqrestore(&sem->lock, flags);

and now we have an existing known-good implementation to look at?

Rather than making up a totally new and untested thing.

		Linus
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