From: Paolo Bonzini <pbonzini@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>, qemu-devel@nongnu.org
Cc: mttcg@greensocs.com, peter.maydell@linaro.org,
mark.burton@greensocs.com, a.rigo@virtualopensystems.com,
stefanha@redhat.com, fred.konrad@greensocs.com
Subject: Re: [Qemu-devel] [PATCH v1 3/5] include/qemu/atomic.h: default to __atomic functions
Date: Thu, 28 Jan 2016 12:00:10 +0100 [thread overview]
Message-ID: <56A9F4BA.1030508@redhat.com> (raw)
In-Reply-To: <1453976119-24372-4-git-send-email-alex.bennee@linaro.org>
On 28/01/2016 11:15, Alex Bennée wrote:
> +/* atomic_mb_read/set semantics map Java volatile variables. They are
> + * less expensive on some platforms (notably POWER & ARM) than fully
> + * sequentially consistent operations.
> + *
> + * As long as they are used as paired operations they are safe to
> + * use. See docs/atomic.txt for more discussion.
> + */
> +
> +#define atomic_mb_read(ptr) \
> + ({ \
> + typeof(*ptr) _val; \
> + __atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
> + smp_rmb(); \
> + _val; \
> + })
> +
> +#define atomic_mb_set(ptr, i) do { \
> + typeof(*ptr) _val = (i); \
> + smp_wmb(); \
> + __atomic_store(ptr, &_val, __ATOMIC_RELAXED); \
> + smp_mb(); \
> +} while(0)
Great... I'll change this to
#if defined(_ARCH_PPC)
#define atomic_mb_read(ptr) \
({ \
typeof(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_RELAXED); \
smp_rmb(); \
_val; \
})
#define atomic_mb_set(ptr, i) do { \
typeof(*ptr) _val = (i); \
smp_wmb(); \
__atomic_store(ptr, &_val, __ATOMIC_RELAXED); \
smp_mb(); \
} while(0)
#else
#define atomic_mb_read(ptr) \
({ \
typeof(*ptr) _val; \
__atomic_load(ptr, &_val, __ATOMIC_SEQ_CST); \
_val; \
})
#define atomic_mb_set(ptr, i) do { \
typeof(*ptr) _val = (i); \
__atomic_store(ptr, &_val, __ATOMIC_SEQ_CST); \
} while(0)
#endif
since this benefits x86 (which can generate mov/xchg respectively) and
aarch64 (where atomic_mb_read/atomic_mb_set map directly to ldar/stlr).
> +/* Returns the eventual value, failed or not */
> +#define atomic_cmpxchg(ptr, old, new) \
> + ({ \
> + typeof(*ptr) _old = (old), _new = (new); \
> + __atomic_compare_exchange(ptr, &_old, &_new, false, \
> + __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
> + _old; /* can this race if cmpxchg not used elsewhere? */ \
> + })
How so?
Paolo
next prev parent reply other threads:[~2016-01-28 11:00 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-28 10:15 [Qemu-devel] [PATCH v1 0/5] ThreadSanitizer support Alex Bennée
2016-01-28 10:15 ` [Qemu-devel] [PATCH v1 1/5] configure: introduce --extra-libs Alex Bennée
2016-01-28 11:14 ` Paolo Bonzini
2016-01-28 11:38 ` Alex Bennée
2016-01-28 10:15 ` [Qemu-devel] [PATCH v1 2/5] configure: ensure ldflags propagated to config_host Alex Bennée
2016-01-28 11:10 ` Paolo Bonzini
2016-01-28 11:13 ` Paolo Bonzini
2016-01-29 15:26 ` Alex Bennée
2016-01-28 10:15 ` [Qemu-devel] [PATCH v1 3/5] include/qemu/atomic.h: default to __atomic functions Alex Bennée
2016-01-28 11:00 ` Paolo Bonzini [this message]
2016-01-29 16:06 ` Alex Bennée
2016-02-04 12:40 ` Paolo Bonzini
2016-02-04 13:00 ` Peter Maydell
2016-04-01 14:30 ` James Hogan
2016-04-01 14:51 ` Peter Maydell
2016-04-01 16:06 ` Alex Bennée
2016-04-01 20:35 ` Pranith Kumar
2016-04-04 8:14 ` Paolo Bonzini
2016-04-04 16:26 ` Pranith Kumar
2016-04-04 17:03 ` Paolo Bonzini
2016-04-04 20:15 ` Paolo Bonzini
2016-04-05 3:35 ` Pranith Kumar
2016-04-05 12:47 ` Paolo Bonzini
2016-01-28 10:15 ` [Qemu-devel] [PATCH v1 4/5] async.c: various atomic fixes for tsan Alex Bennée
2016-01-28 10:45 ` Paolo Bonzini
2016-01-28 10:15 ` [Qemu-devel] [PATCH v1 5/5] thread-pool: atomic fixes from tsan Alex Bennée
2016-01-28 10:44 ` Paolo Bonzini
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