On Tue, 6 May 2008 19:49:54 +0200 Ingo Molnar <mingo@xxxxxxx> wrote: > > * Matthew Wilcox <matthew@xxxxxx> wrote: > > > > down(), down_interruptible() and down_try() should use > > > spin_lock_irq(), not irqsave. > > > > We talked about this ... the BKL actually requires that you be able to > > acquire it with interrupts disabled. [...] > > hm, where does it require it, besides the early bootup code? (which > should just be fixed) Yeah, the early bootup code. The kernel does accidental lock_kernel()s in various places and if that renables interrupts then powerpc goeth crunch. Matthew, that seemingly-unneeded irqsave in lib/semaphore.c is a prime site for /* one of these things */, no? > down_trylock() is OK as irqsave/irqrestore for legacy reasons, but that > is fundamentally atomic anyway. yes, trylock should be made irq-safe. > > > up() seems to be doing wake-one, FIFO which is nice. Did the > > > implementation which we just removed also do that? Was it perhaps > > > accidentally doing LIFO or something like that? > > > > That's a question for someone who knows x86 assembler, I think. > > the assembly is mostly just for the fastpath - and a 40% regression > cannot be about fastpath differences. In the old code the scheduling > happens in lib/semaphore-sleeper.c, and from the looks of it it appears > to be a proper FIFO as well. (plus this small wakeup weirdness it has) > > i reviewed the new code in kernel/semaphore.c as well and can see > nothing bad in it - it does proper wake-up, FIFO queueing, like the > mutex code. > There's the weird wakeup in down() which I understood for about five minutes five years ago. Perhaps that accidentally sped something up. Oh well, more investigation needed.. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
