make spin_lock_prefetch a noop for UP
PATCH 1/1 make spin_lock_prefetch a noop for UP
Is this any good?
The counter argument would be that one might prefetch a spinlock in the head of a data structure, and expect the rest of the cacheline to be in cache as well. Though in that case, maybe prefetch/prefetchw should be used instead.
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SUSE Labs, Novell Inc.
#define spin_lock_prefetch to be a noop on UP builds.
Also, make architectures that define spin_lock_prefetch to be prefetchw just use the generic spin_lock_prefetch.
include/asm-i386/processor.h +0 -2
@@ -673,7 +673,6 @@ extern inline void prefetch(const void *#define ARCH_HAS_PREFETCH #define ARCH_HAS_PREFETCHW -#define ARCH_HAS_SPINLOCK_PREFETCH /* 3dnow! prefetch to get an exclusive cache line. Useful for spinlocks to avoid one state transition in the cache coherency protocol. */
@@ -684,7 +683,6 @@ extern inline void prefetchw(const voidX86_FEATURE_3DNOW , "r" (x)); } -#define spin_lock_prefetch (x) prefetchw(x)extern void select_idle_routine (const struct cpuinfo_x86 *c);
include/asm-ia64/processor.h +0 -3
@@ -676,7 +676,6 @@ ia64_imva (void *addr)#define ARCH_HAS_PREFETCH #define ARCH_HAS_PREFETCHW -#define ARCH_HAS_SPINLOCK_PREFETCH #define PREFETCH_STRIDE L1_CACHE_BYTES static inline void
@@ -691,8 +690,6 @@ prefetchw (const void *x) ia64_lfetch_excl(ia64_lfhint_none, x); } -#define spin_lock_prefetch (x) prefetchw(x) -extern unsigned long boot_option_idle_override;#endif /* !__ASSEMBLY__ */
include/asm-ppc/processor.h +0 -3
@@ -179,7 +179,6 @@ void _nmask_and_or_msr(unsigned long nma*/ #define ARCH_HAS_PREFETCH #define ARCH_HAS_PREFETCHW -#define ARCH_HAS_SPINLOCK_PREFETCH extern inline void prefetch (const void *x) {
@@ -191,8 +190,6 @@ extern inline void prefetchw(const void __asm__ __volatile__ ("dcbtst 0,%0" : : "r" (x)); } -#define spin_lock_prefetch (x) prefetchw(x) -extern int emulate_altivec (struct pt_regs *regs);#endif /* !__ASSEMBLY__ */
include/asm-ppc64/processor.h +0 -3
@@ -476,7 +476,6 @@ static inline unsigned long __pack_fe01(*/ #define ARCH_HAS_PREFETCH #define ARCH_HAS_PREFETCHW -#define ARCH_HAS_SPINLOCK_PREFETCH static inline void prefetch (const void *x) {
@@ -494,8 +493,6 @@ static inline void prefetchw(const void __asm__ __volatile__ ("dcbtst 0,%0" : :"r" (x)); } -#define spin_lock_prefetch (x) prefetchw(x) -#define HAVE_ARCH_PICK_MMAP_LAYOUT static inline void ppc64_runlatch_on (void )
include/asm-sparc64/processor.h +0 -3
@@ -198,7 +198,6 @@ extern unsigned long get_wchan(struct ta*/ #define ARCH_HAS_PREFETCH #define ARCH_HAS_PREFETCHW -#define ARCH_HAS_SPINLOCK_PREFETCH static inline void prefetch (const void *x) {
@@ -224,8 +223,6 @@ static inline void prefetchw(const void : "r" (x)); } -#define spin_lock_prefetch (x) prefetchw(x) -#endif /* !(__ASSEMBLY__) */ #endif /* !(__ASM_SPARC64_PROCESSOR_H) */
include/asm-x86_64/processor.h +0 -4
@@ -404,10 +404,6 @@ static inline void prefetchw(void *x) "r" (x)); } -#define ARCH_HAS_SPINLOCK_PREFETCH 1 - -#define spin_lock_prefetch (x) prefetchw(x) -#define cpu_relax () rep_nop()/*
include/linux/prefetch.h +4 -0
@@ -48,7 +48,11 @@ static inline void prefetchw(const void#endif #ifndef ARCH_HAS_SPINLOCK_PREFETCH +#ifdef CONFIG_SMP #define spin_lock_prefetch (x) prefetchw(x) +#else +#define spin_lock_prefetch (x) +#endif #endif #ifndef PREFETCH_STRIDE
Quoted 7 lines · Nick Piggin
Is this any good?
The counter argument would be that one might prefetch a spinlock in the head of a data structure, and expect the rest of the cacheline to be in cache as well. Though in that case, maybe prefetch/prefetchw should be used instead.
Can you describe what the supposed improvement of the patch is?
-Andi
Quoted 4 lines · Andi Kleen
Quoted 2 lines · Nick Piggin
Is this any good?
Quoted 9 lines
Quoted 5 lines
The counter argument would be that one might prefetch a spinlock in the head of a data structure, and expect the rest of the cacheline to be in cache as well. Though in that case, maybe prefetch/prefetchw should be used instead.
Can you describe what the supposed improvement of the patch is?
From include/linux/prefetch.h:
"spin_lock_prefetch(x) - prefectches the spinlock *x for taking"
So this would reduce icache footprint and possibly memory traffic on UP where taking a spinlock is a noop.
Granted, there aren't many users of spin_lock_prefetch at the moment.
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SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com
Quoted 6 lines
From
include/linux/prefetch.h:"
spin_lock_prefetch(x)- prefectches the spinlock *x for taking"So this would reduce icache footprint and possibly memory traffic on UP where taking a spinlock is a noop.
Ah you want to disable it on UP?
Ok that makes more sense. Why didn't you just say that? :)
Anyways, even on UP it might be useful on all these mutex or whatever lock is envogue these days preemptive kernels.
-Andi
Quoted 10 lines · Andi Kleen
Quoted 6 lines
From
include/linux/prefetch.h:"
spin_lock_prefetch(x)- prefectches the spinlock *x for taking"So this would reduce icache footprint and possibly memory traffic on UP where taking a spinlock is a noop.
Ah you want to disable it on UP? Ok that makes more sense. Why didn't you just say that? :)
Well I did, in a confusing kind of way ;) ... with the alternative input stuff being used here, "noop" becomes ambiguous I guess.
Quoted 3 lines
Anyways, even on UP it might be useful on all these mutex or whatever lock is envogue these days preemptive kernels.
I'm sure it would be useful. Though it is something that could be maintained out of tree.
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SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com