From mboxrd@z Thu Jan 1 00:00:00 1970 From: nathan.sullivan@ni.com (Nathan Sullivan) Date: Thu, 29 Jan 2015 12:56:18 -0600 Subject: __HAVE_ARCH_CMPXCHG on ARM? Message-ID: <20150129185618.GA31459@nathan3500-linux-VM> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 patch with a fixed s-o-b? Thanks! Nathan Sullivan [1]: http://lists.infradead.org/pipermail/linux-arm-kernel/2012-May/102122.html (duplicated below) -- 8< -- From: Yong Zhang Both pi_stress and sigwaittest in rt-test show performance gain with __HAVE_ARCH_CMPXCHG. Testing result on coretile_express_a9x4: pi_stress -p 99 --duration=300 (on linux-3.4-rc5; bigger is better) vanilla: Total inversion performed: 5493381 patched: Total inversion performed: 5621746 sigwaittest -p 99 -l 100000 (on linux-3.4-rc5-rt6; less is better) 3.4-rc5-rt6: Min 24, Cur 27, Avg 30, Max 98 patched: Min 19, Cur 21, Avg 23, Max 96 Signed-off-by: Yong Zhang Cc: Russell King Cc: Nicolas Pitre Cc: Will Deacon Cc: Catalin Marinas Cc: Thomas Gleixner Cc: linux-arm-kernel at lists.infradead.org --- arch/arm/include/asm/cmpxchg.h | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) 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 + extern void __bad_cmpxchg(volatile void *ptr, int size); /* -- 1.7.5.4