From 4e14a4d17a8cd66ccab180d32c977091922cfbed Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Wed, 10 Feb 2010 00:57:28 +0000 Subject: powerpc: Use lwarx hint in spinlocks Recent versions of the PowerPC architecture added a hint bit to the larx instructions to differentiate between an atomic operation and a lock operation: > 0 Other programs might attempt to modify the word in storage addressed by EA > even if the subsequent Store Conditional succeeds. > > 1 Other programs will not attempt to modify the word in storage addressed by > EA until the program that has acquired the lock performs a subsequent store > releasing the lock. To avoid a binutils dependency this patch create macros for the extended lwarx format and uses it in the spinlock code. To test this change I used a simple test case that acquires and releases a global pthread mutex: pthread_mutex_lock(&mutex); pthread_mutex_unlock(&mutex); On a 32 core POWER6, running 32 test threads we spend almost all our time in the futex spinlock code: 94.37% perf [kernel] [k] ._raw_spin_lock | |--99.95%-- ._raw_spin_lock | | | |--63.29%-- .futex_wake | | | |--36.64%-- .futex_wait_setup Which is a good test for this patch. The results (in lock/unlock operations per second) are: before: 1538203 ops/sec after: 2189219 ops/sec An improvement of 42% A 32 core POWER7 improves even more: before: 1279529 ops/sec after: 2282076 ops/sec An improvement of 78% Signed-off-by: Anton Blanchard Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/include/asm/ppc-opcode.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'arch/powerpc/include/asm/ppc-opcode.h') diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h index ef9aa84cac5a..ecec76051184 100644 --- a/arch/powerpc/include/asm/ppc-opcode.h +++ b/arch/powerpc/include/asm/ppc-opcode.h @@ -24,6 +24,7 @@ #define PPC_INST_ISEL_MASK 0xfc00003e #define PPC_INST_LSWI 0x7c0004aa #define PPC_INST_LSWX 0x7c00042a +#define PPC_INST_LWARX 0x7c000029 #define PPC_INST_LWSYNC 0x7c2004ac #define PPC_INST_LXVD2X 0x7c000698 #define PPC_INST_MCRXR 0x7c000400 @@ -55,15 +56,28 @@ #define __PPC_RA(a) (((a) & 0x1f) << 16) #define __PPC_RB(b) (((b) & 0x1f) << 11) #define __PPC_RS(s) (((s) & 0x1f) << 21) +#define __PPC_RT(s) __PPC_RS(s) #define __PPC_XS(s) ((((s) & 0x1f) << 21) | (((s) & 0x20) >> 5)) #define __PPC_T_TLB(t) (((t) & 0x3) << 21) #define __PPC_WC(w) (((w) & 0x3) << 21) +/* + * Only use the larx hint bit on 64bit CPUs. Once we verify it doesn't have + * any side effects on all 32bit processors, we can do this all the time. + */ +#ifdef CONFIG_PPC64 +#define __PPC_EH(eh) (((eh) & 0x1) << 0) +#else +#define __PPC_EH(eh) 0 +#endif /* Deal with instructions that older assemblers aren't aware of */ #define PPC_DCBAL(a, b) stringify_in_c(.long PPC_INST_DCBAL | \ __PPC_RA(a) | __PPC_RB(b)) #define PPC_DCBZL(a, b) stringify_in_c(.long PPC_INST_DCBZL | \ __PPC_RA(a) | __PPC_RB(b)) +#define PPC_LWARX(t, a, b, eh) stringify_in_c(.long PPC_INST_LWARX | \ + __PPC_RT(t) | __PPC_RA(a) | \ + __PPC_RB(b) | __PPC_EH(eh)) #define PPC_MSGSND(b) stringify_in_c(.long PPC_INST_MSGSND | \ __PPC_RB(b)) #define PPC_RFCI stringify_in_c(.long PPC_INST_RFCI) -- cgit v1.2.3