From 93ea02bb84354370e51de803a9405f171f3edf88 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 6 Nov 2013 14:57:36 +0100 Subject: arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h We're going to be adding a few new barrier primitives, and in order to avoid endless duplication make more agressive use of asm-generic/barrier.h. Change the asm-generic/barrier.h such that it allows partial barrier definitions and fills out the rest with defaults. There are a few architectures (m32r, m68k) that could probably do away with their barrier.h file entirely but are kept for now due to their unconventional nop() implementation. Suggested-by: Geert Uytterhoeven Reviewed-by: "Paul E. McKenney" Reviewed-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra Cc: Michael Ellerman Cc: Michael Neuling Cc: Russell King Cc: Heiko Carstens Cc: Linus Torvalds Cc: Martin Schwidefsky Cc: Victor Kaplansky Cc: Tony Luck Cc: Oleg Nesterov Cc: Benjamin Herrenschmidt Cc: Frederic Weisbecker Link: http://lkml.kernel.org/r/20131213150640.846368594@infradead.org Signed-off-by: Ingo Molnar --- arch/sparc/include/asm/barrier_32.h | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) (limited to 'arch/sparc') diff --git a/arch/sparc/include/asm/barrier_32.h b/arch/sparc/include/asm/barrier_32.h index c1b76654ee76..ae69eda288f4 100644 --- a/arch/sparc/include/asm/barrier_32.h +++ b/arch/sparc/include/asm/barrier_32.h @@ -1,15 +1,7 @@ #ifndef __SPARC_BARRIER_H #define __SPARC_BARRIER_H -/* XXX Change this if we ever use a PSO mode kernel. */ -#define mb() __asm__ __volatile__ ("" : : : "memory") -#define rmb() mb() -#define wmb() mb() -#define read_barrier_depends() do { } while(0) -#define set_mb(__var, __value) do { __var = __value; mb(); } while(0) -#define smp_mb() __asm__ __volatile__("":::"memory") -#define smp_rmb() __asm__ __volatile__("":::"memory") -#define smp_wmb() __asm__ __volatile__("":::"memory") -#define smp_read_barrier_depends() do { } while(0) +#include /* for nop() */ +#include #endif /* !(__SPARC_BARRIER_H) */ -- cgit v1.2.3 From 47933ad41a86a4a9b50bed7c9b9bd2ba242aac63 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 6 Nov 2013 14:57:36 +0100 Subject: arch: Introduce smp_load_acquire(), smp_store_release() A number of situations currently require the heavyweight smp_mb(), even though there is no need to order prior stores against later loads. Many architectures have much cheaper ways to handle these situations, but the Linux kernel currently has no portable way to make use of them. This commit therefore supplies smp_load_acquire() and smp_store_release() to remedy this situation. The new smp_load_acquire() primitive orders the specified load against any subsequent reads or writes, while the new smp_store_release() primitive orders the specifed store against any prior reads or writes. These primitives allow array-based circular FIFOs to be implemented without an smp_mb(), and also allow a theoretical hole in rcu_assign_pointer() to be closed at no additional expense on most architectures. In addition, the RCU experience transitioning from explicit smp_read_barrier_depends() and smp_wmb() to rcu_dereference() and rcu_assign_pointer(), respectively resulted in substantial improvements in readability. It therefore seems likely that replacing other explicit barriers with smp_load_acquire() and smp_store_release() will provide similar benefits. It appears that roughly half of the explicit barriers in core kernel code might be so replaced. [Changelog by PaulMck] Reviewed-by: "Paul E. McKenney" Signed-off-by: Peter Zijlstra Acked-by: Will Deacon Cc: Benjamin Herrenschmidt Cc: Frederic Weisbecker Cc: Mathieu Desnoyers Cc: Michael Ellerman Cc: Michael Neuling Cc: Russell King Cc: Geert Uytterhoeven Cc: Heiko Carstens Cc: Linus Torvalds Cc: Martin Schwidefsky Cc: Victor Kaplansky Cc: Tony Luck Cc: Oleg Nesterov Link: http://lkml.kernel.org/r/20131213150640.908486364@infradead.org Signed-off-by: Ingo Molnar --- arch/sparc/include/asm/barrier_64.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'arch/sparc') diff --git a/arch/sparc/include/asm/barrier_64.h b/arch/sparc/include/asm/barrier_64.h index 95d45986f908..b5aad964558e 100644 --- a/arch/sparc/include/asm/barrier_64.h +++ b/arch/sparc/include/asm/barrier_64.h @@ -53,4 +53,19 @@ do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \ #define smp_read_barrier_depends() do { } while(0) +#define smp_store_release(p, v) \ +do { \ + compiletime_assert_atomic_type(*p); \ + barrier(); \ + ACCESS_ONCE(*p) = (v); \ +} while (0) + +#define smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = ACCESS_ONCE(*p); \ + compiletime_assert_atomic_type(*p); \ + barrier(); \ + ___p1; \ +}) + #endif /* !(__SPARC64_BARRIER_H) */ -- cgit v1.2.3