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On !SMP, most architectures define their barriers as compiler barriers. On SMP, most need an actual barrier. Make it possible to remove the code duplication for !SMP by defining low-level __smp_xxx barriers which do not depend on the value of SMP, then use them from asm-generic conditionally. Besides reducing code duplication, these low level APIs will also be useful for virtualization, where a barrier is sometimes needed even if !SMP since we might be talking to another kernel on the same SMP system. Both virtio and Xen drivers will benefit. The smp_xxx variants should use __smp_XXX ones or barrier() depending on SMP, identically for all architectures. We keep ifndef guards around them for now - once/if all architectures are converted to use the generic code, we'll be able to remove these. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Acked-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
200 lines
3.9 KiB
C
200 lines
3.9 KiB
C
/*
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* Generic barrier definitions, originally based on MN10300 definitions.
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*
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* It should be possible to use these on really simple architectures,
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* but it serves more as a starting point for new ports.
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*
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* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#ifndef __ASM_GENERIC_BARRIER_H
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#define __ASM_GENERIC_BARRIER_H
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#ifndef __ASSEMBLY__
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#include <linux/compiler.h>
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#ifndef nop
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#define nop() asm volatile ("nop")
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#endif
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/*
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* Force strict CPU ordering. And yes, this is required on UP too when we're
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* talking to devices.
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*
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* Fall back to compiler barriers if nothing better is provided.
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*/
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#ifndef mb
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#define mb() barrier()
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#endif
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#ifndef rmb
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#define rmb() mb()
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#endif
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#ifndef wmb
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#define wmb() mb()
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#endif
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#ifndef dma_rmb
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#define dma_rmb() rmb()
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#endif
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#ifndef dma_wmb
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#define dma_wmb() wmb()
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#endif
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#ifndef read_barrier_depends
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#define read_barrier_depends() do { } while (0)
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#endif
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#ifndef __smp_mb
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#define __smp_mb() mb()
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#endif
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#ifndef __smp_rmb
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#define __smp_rmb() rmb()
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#endif
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#ifndef __smp_wmb
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#define __smp_wmb() wmb()
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#endif
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#ifndef __smp_read_barrier_depends
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#define __smp_read_barrier_depends() read_barrier_depends()
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#endif
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#ifdef CONFIG_SMP
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#ifndef smp_mb
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#define smp_mb() __smp_mb()
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#endif
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#ifndef smp_rmb
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#define smp_rmb() __smp_rmb()
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#endif
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#ifndef smp_wmb
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#define smp_wmb() __smp_wmb()
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#endif
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#ifndef smp_read_barrier_depends
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#define smp_read_barrier_depends() __smp_read_barrier_depends()
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#endif
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#else /* !CONFIG_SMP */
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#ifndef smp_mb
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#define smp_mb() barrier()
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#endif
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#ifndef smp_rmb
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#define smp_rmb() barrier()
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#endif
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#ifndef smp_wmb
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#define smp_wmb() barrier()
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#endif
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#ifndef smp_read_barrier_depends
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#define smp_read_barrier_depends() do { } while (0)
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#endif
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#endif /* CONFIG_SMP */
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#ifndef __smp_store_mb
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#define __smp_store_mb(var, value) do { WRITE_ONCE(var, value); __smp_mb(); } while (0)
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#endif
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#ifndef __smp_mb__before_atomic
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#define __smp_mb__before_atomic() __smp_mb()
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#endif
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#ifndef __smp_mb__after_atomic
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#define __smp_mb__after_atomic() __smp_mb()
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#endif
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#ifndef __smp_store_release
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#define __smp_store_release(p, v) \
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do { \
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compiletime_assert_atomic_type(*p); \
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__smp_mb(); \
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WRITE_ONCE(*p, v); \
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} while (0)
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#endif
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#ifndef __smp_load_acquire
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#define __smp_load_acquire(p) \
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({ \
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typeof(*p) ___p1 = READ_ONCE(*p); \
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compiletime_assert_atomic_type(*p); \
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__smp_mb(); \
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___p1; \
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})
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#endif
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#ifdef CONFIG_SMP
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#ifndef smp_store_mb
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#define smp_store_mb(var, value) __smp_store_mb(var, value)
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#endif
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#ifndef smp_mb__before_atomic
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#define smp_mb__before_atomic() __smp_mb__before_atomic()
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#endif
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#ifndef smp_mb__after_atomic
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#define smp_mb__after_atomic() __smp_mb__after_atomic()
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#endif
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#ifndef smp_store_release
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#define smp_store_release(p, v) __smp_store_release(p, v)
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#endif
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#ifndef smp_load_acquire
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#define smp_load_acquire(p) __smp_load_acquire(p)
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#endif
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#else /* !CONFIG_SMP */
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#ifndef smp_store_mb
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#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); } while (0)
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#endif
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#ifndef smp_mb__before_atomic
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#define smp_mb__before_atomic() barrier()
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#endif
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#ifndef smp_mb__after_atomic
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#define smp_mb__after_atomic() barrier()
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#endif
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#ifndef smp_store_release
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#define smp_store_release(p, v) \
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do { \
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compiletime_assert_atomic_type(*p); \
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barrier(); \
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WRITE_ONCE(*p, v); \
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} while (0)
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#endif
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#ifndef smp_load_acquire
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#define smp_load_acquire(p) \
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({ \
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typeof(*p) ___p1 = READ_ONCE(*p); \
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compiletime_assert_atomic_type(*p); \
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barrier(); \
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___p1; \
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})
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#endif
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#endif
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#endif /* !__ASSEMBLY__ */
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#endif /* __ASM_GENERIC_BARRIER_H */
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