On Thu, Apr 01, 2010 at 10:41:11AM +0100, Jamie Lokier wrote: > David Howells wrote: > > Russell King <rmk@xxxxxxxxxxxxxxxx> wrote: > > > We use the standard generic kernel implementation. Is x86 different? ;) > > > > The optimised fast paths used on x86 rwsems don't disable interrupts. > > Any reason not to use the same technique for all the archs - plus the > trick used in arch/armkernel/entry-armv.S:__kuser_cmpxchg for those > archs which don't have atomic instructions or ll/sc? Assuming you're talking about the __LINUX_ARM_ARCH__ < 6 + CONFIG_MMU case, then this only works for uniprocessor machines. > If the problem here is _only_ semaphores, and the above might make > semaphores faster anyway, perhaps it's a solution. You trade off a bit of overhead in the semaphore path for a bit of overhead in the interrupt path. We probably take more sempahores than we do interrupts, so it's probably worthwhile. Still, cmpxchg() needs to be SMP-safe. Realistically, this isn't something that can be done in generic code. It has to be done in arch-specific code. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
