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 <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index 764094c..1c35b59 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -27,6 +27,7 @@
#endif
#include <asm/asm-compat.h>
#include <asm/synch.h>
+#include <asm/ppc-opcode.h>
#define arch_spin_is_locked(x) ((x)->slock != 0)
@@ -60,7 +61,7 @@
token = LOCK_TOKEN;
__asm__ __volatile__(
-"1: lwarx %0,0,%2\n\
+"1: " PPC_LWARX(%0,0,%2,1) "\n\
cmpwi 0,%0,0\n\
bne- 2f\n\
stwcx. %1,0,%2\n\
@@ -186,7 +187,7 @@
long tmp;
__asm__ __volatile__(
-"1: lwarx %0,0,%1\n"
+"1: " PPC_LWARX(%0,0,%1,1) "\n"
__DO_SIGN_EXTEND
" addic. %0,%0,1\n\
ble- 2f\n"
@@ -211,7 +212,7 @@
token = WRLOCK_TOKEN;
__asm__ __volatile__(
-"1: lwarx %0,0,%2\n\
+"1: " PPC_LWARX(%0,0,%2,1) "\n\
cmpwi 0,%0,0\n\
bne- 2f\n"
PPC405_ERR77(0,%1)