On Mon, Feb 02, 2015 at 01:39:33PM +0000, Will Deacon wrote: > On Fri, Jan 30, 2015 at 08:44:48AM +0000, Yong Zhang wrote: > > On Fri, Jan 30, 2015 at 2:56 AM, Nathan Sullivan <nathan.sullivan@xxxxxx<mailto:nathan.sullivan@xxxxxx>> wrote: > > > > While investigating a performance issue on RT 3.14, I noticed that > > __HAVE_ARCH_CMPXCHG is not defined for ARM. This causes -rt locks to > > always use the slow path and impacts performance. ARMv6 and above > > have a cmpxchg implementation already that will work just fine. > > > > In 2012, Yong Zhang submitted a patch to fix this[1], but it mysteriously > > disappeared afterwards. I did notice that the s-o-b line has a different > > email address than the windriver one. Yong, do you mind re-submitting the > > > > It actually doesn't matter. Anyway feel free to add another s-o-b to > > the patch: > > > > Signed-off-by: Yong Zhang <yong.zhang@xxxxxxxxxxxxx<mailto:yong.zhang@xxxxxxxxxxxxx>> > > [...] > > > diff --git a/arch/arm/include/asm/cmpxchg.h b/arch/arm/include/asm/cmpxchg.h > > index 7eb18c1..a91b44e 100644 > > --- a/arch/arm/include/asm/cmpxchg.h > > +++ b/arch/arm/include/asm/cmpxchg.h > > @@ -127,6 +127,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size > > > > #else /* min ARCH >= ARMv6 */ > > > > +#define __HAVE_ARCH_CMPXCHG 1 > > Is it even possible to have CONFIG_SMP=y on an architecture that doesn't > support native cmpxchg? Certainly, the asm-generic cmpxchg.h barfs if > SMP, so couldn't we just change/extend the __HAVE_ARCH_CMPXCHG check in > rtmutex.c to work automatically with SMP architectures? That would help > arm64 too. > > Will What about single Cortex-A8s, for example? Seems like a non-SMP build should still have cmpxchg. Nathan -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
