On Thu, 2008-03-20 at 09:04 -0700, Luck, Tony wrote: > > Which makes me wonder, why did you ever use a semaphore here? Looking at > > the code its a straight forward mutex. And when you would have used a > > mutex lockdep would have warned about this. > > The functionality that we are trying to add is to allow up to N > simultaneous processors to execute the critical region. On current > processors/platforms N=1 so a spinlock or mutex would be fine, but > there will be platforms for which N is a small integer greater than > one. Semaphore initialized to N looked to be the ideal primitive > for this (until Motohiro-san ran the test case that showed the path > where we call this code with a spinlock held). Right, no alternative there. > Next question is whether it is reasonable to get to this code > while holding a spinlock. Isn't this a problem for architectures > that need to use cross-processor interrupts to do a global TLB > shootdown? Yeah, semaphores can't be used from hardirq contexts for much the same reasons. But its all ia64 code, right? So I'm not directly seeing how other archs are affected here. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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