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Date: Mon, 3 Aug 2015 19:21:34 +0100
From: Will Deacon <will.deacon@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
"Waiman.Long@...com" <Waiman.Long@...com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
"mingo@...nel.org" <mingo@...nel.org>
Subject: Re: [PATCH v4 1/8] atomics: add acquire/release/relaxed variants of
some atomic operations
On Mon, Aug 03, 2015 at 06:26:58PM +0100, Peter Zijlstra wrote:
> On Mon, Aug 03, 2015 at 06:02:24PM +0100, Will Deacon wrote:
> > +/*
> > + * The idea here is to build acquire/release variants by adding explicit
> > + * barriers on top of the relaxed variant. In the case where the relaxed
> > + * variant is already fully ordered, no additional barriers are needed.
> > + */
> > +#define __atomic_op_acquire(ret_t, op, ...) \
> > +({ \
> > + ret_t __ret = op##_relaxed(__VA_ARGS__); \
>
> Do you really need ret_t? Can't we use typeof() on the expression?
*gulp*! I was slightly worried about this from the GNU docs:
`The operand of typeof is evaluated for its side effects if and only if
it is an expression of variably modified type or the name of such a
type.'
but since none of our atomic functions return "variably modified types",
then there shouldn't be anything to worry about. It also means I can
slightly simplify the xchg/cmpxchg wrappers where we were previously
passing through the typeof(*ptr).
Incremental diff below (I'll post a v5 when the build testing comes back
clean).
Will
--->8
diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index d2515c05e7c8..41ea776052be 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -35,26 +35,24 @@
* barriers on top of the relaxed variant. In the case where the relaxed
* variant is already fully ordered, no additional barriers are needed.
*/
-#define __atomic_op_acquire(ret_t, op, ...) \
+#define __atomic_op_acquire(op, args...) \
({ \
- ret_t __ret = op##_relaxed(__VA_ARGS__); \
+ typeof(op##_relaxed(args)) __ret = op##_relaxed(args); \
smp_mb__after_atomic(); \
__ret; \
})
-#define __atomic_op_release(ret_t, op, ...) \
+#define __atomic_op_release(op, args...) \
({ \
- ret_t __ret; \
smp_mb__before_atomic(); \
- __ret = op##_relaxed(__VA_ARGS__); \
- __ret; \
+ op##_relaxed(args); \
})
-#define __atomic_op_fence(ret_t, op, ...) \
+#define __atomic_op_fence(op, args...) \
({ \
- ret_t __ret; \
+ typeof(op##_relaxed(args)) __ret; \
smp_mb__before_atomic(); \
- __ret = op##_relaxed(__VA_ARGS__); \
+ __ret = op##_relaxed(args); \
smp_mb__after_atomic(); \
__ret; \
})
@@ -69,17 +67,17 @@
#ifndef atomic_add_return_acquire
#define atomic_add_return_acquire(...) \
- __atomic_op_acquire(int, atomic_add_return, __VA_ARGS__)
+ __atomic_op_acquire(atomic_add_return, __VA_ARGS__)
#endif
#ifndef atomic_add_return_release
#define atomic_add_return_release(...) \
- __atomic_op_release(int, atomic_add_return, __VA_ARGS__)
+ __atomic_op_release(atomic_add_return, __VA_ARGS__)
#endif
#ifndef atomic_add_return
#define atomic_add_return(...) \
- __atomic_op_fence(int, atomic_add_return, __VA_ARGS__)
+ __atomic_op_fence(atomic_add_return, __VA_ARGS__)
#endif
#endif /* atomic_add_return_relaxed */
@@ -93,17 +91,17 @@
#ifndef atomic_sub_return_acquire
#define atomic_sub_return_acquire(...) \
- __atomic_op_acquire(int, atomic_sub_return, __VA_ARGS__)
+ __atomic_op_acquire(atomic_sub_return, __VA_ARGS__)
#endif
#ifndef atomic_sub_return_release
#define atomic_sub_return_release(...) \
- __atomic_op_release(int, atomic_sub_return, __VA_ARGS__)
+ __atomic_op_release(atomic_sub_return, __VA_ARGS__)
#endif
#ifndef atomic_sub_return
#define atomic_sub_return(...) \
- __atomic_op_fence(int, atomic_sub_return, __VA_ARGS__)
+ __atomic_op_fence(atomic_sub_return, __VA_ARGS__)
#endif
#endif /* atomic_sub_return_relaxed */
@@ -117,17 +115,17 @@
#ifndef atomic_xchg_acquire
#define atomic_xchg_acquire(...) \
- __atomic_op_acquire(int, atomic_xchg, __VA_ARGS__)
+ __atomic_op_acquire(atomic_xchg, __VA_ARGS__)
#endif
#ifndef atomic_xchg_release
#define atomic_xchg_release(...) \
- __atomic_op_release(int, atomic_xchg, __VA_ARGS__)
+ __atomic_op_release(atomic_xchg, __VA_ARGS__)
#endif
#ifndef atomic_xchg
#define atomic_xchg(...) \
- __atomic_op_fence(int, atomic_xchg, __VA_ARGS__)
+ __atomic_op_fence(atomic_xchg, __VA_ARGS__)
#endif
#endif /* atomic_xchg_relaxed */
@@ -141,17 +139,17 @@
#ifndef atomic_cmpxchg_acquire
#define atomic_cmpxchg_acquire(...) \
- __atomic_op_acquire(int, atomic_cmpxchg, __VA_ARGS__)
+ __atomic_op_acquire(atomic_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic_cmpxchg_release
#define atomic_cmpxchg_release(...) \
- __atomic_op_release(int, atomic_cmpxchg, __VA_ARGS__)
+ __atomic_op_release(atomic_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic_cmpxchg
#define atomic_cmpxchg(...) \
- __atomic_op_fence(int, atomic_cmpxchg, __VA_ARGS__)
+ __atomic_op_fence(atomic_cmpxchg, __VA_ARGS__)
#endif
#endif /* atomic_cmpxchg_relaxed */
@@ -173,17 +171,17 @@
#ifndef atomic64_add_return_acquire
#define atomic64_add_return_acquire(...) \
- __atomic_op_acquire(long long, atomic64_add_return, __VA_ARGS__)
+ __atomic_op_acquire(atomic64_add_return, __VA_ARGS__)
#endif
#ifndef atomic64_add_return_release
#define atomic64_add_return_release(...) \
- __atomic_op_release(long long, atomic64_add_return, __VA_ARGS__)
+ __atomic_op_release(atomic64_add_return, __VA_ARGS__)
#endif
#ifndef atomic64_add_return
#define atomic64_add_return(...) \
- __atomic_op_fence(long long, atomic64_add_return, __VA_ARGS__)
+ __atomic_op_fence(atomic64_add_return, __VA_ARGS__)
#endif
#endif /* atomic64_add_return_relaxed */
@@ -197,17 +195,17 @@
#ifndef atomic64_sub_return_acquire
#define atomic64_sub_return_acquire(...) \
- __atomic_op_acquire(long long, atomic64_sub_return, __VA_ARGS__)
+ __atomic_op_acquire(atomic64_sub_return, __VA_ARGS__)
#endif
#ifndef atomic64_sub_return_release
#define atomic64_sub_return_release(...) \
- __atomic_op_release(long long, atomic64_sub_return, __VA_ARGS__)
+ __atomic_op_release(atomic64_sub_return, __VA_ARGS__)
#endif
#ifndef atomic64_sub_return
#define atomic64_sub_return(...) \
- __atomic_op_fence(long long, atomic64_sub_return, __VA_ARGS__)
+ __atomic_op_fence(atomic64_sub_return, __VA_ARGS__)
#endif
#endif /* atomic64_sub_return_relaxed */
@@ -221,17 +219,17 @@
#ifndef atomic64_xchg_acquire
#define atomic64_xchg_acquire(...) \
- __atomic_op_acquire(long long, atomic64_xchg, __VA_ARGS__)
+ __atomic_op_acquire(atomic64_xchg, __VA_ARGS__)
#endif
#ifndef atomic64_xchg_release
#define atomic64_xchg_release(...) \
- __atomic_op_release(long long, atomic64_xchg, __VA_ARGS__)
+ __atomic_op_release(atomic64_xchg, __VA_ARGS__)
#endif
#ifndef atomic64_xchg
#define atomic64_xchg(...) \
- __atomic_op_fence(long long, atomic64_xchg, __VA_ARGS__)
+ __atomic_op_fence(atomic64_xchg, __VA_ARGS__)
#endif
#endif /* atomic64_xchg_relaxed */
@@ -245,17 +243,17 @@
#ifndef atomic64_cmpxchg_acquire
#define atomic64_cmpxchg_acquire(...) \
- __atomic_op_acquire(long long, atomic64_cmpxchg, __VA_ARGS__)
+ __atomic_op_acquire(atomic64_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic64_cmpxchg_release
#define atomic64_cmpxchg_release(...) \
- __atomic_op_release(long long, atomic64_cmpxchg, __VA_ARGS__)
+ __atomic_op_release(atomic64_cmpxchg, __VA_ARGS__)
#endif
#ifndef atomic64_cmpxchg
#define atomic64_cmpxchg(...) \
- __atomic_op_fence(long long, atomic64_cmpxchg, __VA_ARGS__)
+ __atomic_op_fence(atomic64_cmpxchg, __VA_ARGS__)
#endif
#endif /* atomic64_cmpxchg_relaxed */
@@ -268,18 +266,18 @@
#else /* cmpxchg_relaxed */
#ifndef cmpxchg_acquire
-#define cmpxchg_acquire(ptr, ...) \
- __atomic_op_acquire(__typeof__(*ptr), cmpxchg, ptr, __VA_ARGS__)
+#define cmpxchg_acquire(...) \
+ __atomic_op_acquire(cmpxchg, __VA_ARGS__)
#endif
#ifndef cmpxchg_release
-#define cmpxchg_release(ptr, ...) \
- __atomic_op_release(__typeof__(*ptr), cmpxchg, ptr, __VA_ARGS__)
+#define cmpxchg_release(...) \
+ __atomic_op_release(cmpxchg, __VA_ARGS__)
#endif
#ifndef cmpxchg
-#define cmpxchg(ptr, ...) \
- __atomic_op_fence(__typeof__(*ptr), cmpxchg, ptr, __VA_ARGS__)
+#define cmpxchg(...) \
+ __atomic_op_fence(cmpxchg, __VA_ARGS__)
#endif
#endif /* cmpxchg_relaxed */
@@ -292,18 +290,18 @@
#else /* cmpxchg64_relaxed */
#ifndef cmpxchg64_acquire
-#define cmpxchg64_acquire(ptr, ...) \
- __atomic_op_acquire(__typeof__(*ptr), cmpxchg64, ptr, __VA_ARGS__)
+#define cmpxchg64_acquire(...) \
+ __atomic_op_acquire(cmpxchg64, __VA_ARGS__)
#endif
#ifndef cmpxchg64_release
-#define cmpxchg64_release(ptr, ...) \
- __atomic_op_release(__typeof__(*ptr), cmpxchg64, ptr, __VA_ARGS__)
+#define cmpxchg64_release(...) \
+ __atomic_op_release(cmpxchg64, __VA_ARGS__)
#endif
#ifndef cmpxchg64
-#define cmpxchg64(ptr, ...) \
- __atomic_op_fence(__typeof__(*ptr), cmpxchg64, ptr, __VA_ARGS__)
+#define cmpxchg64(...) \
+ __atomic_op_fence(cmpxchg64, __VA_ARGS__)
#endif
#endif /* cmpxchg64_relaxed */
@@ -316,18 +314,15 @@
#else /* xchg_relaxed */
#ifndef xchg_acquire
-#define xchg_acquire(ptr, ...) \
- __atomic_op_acquire(__typeof__(*ptr), xchg, ptr, __VA_ARGS__)
+#define xchg_acquire(...) __atomic_op_acquire(xchg, __VA_ARGS__)
#endif
#ifndef xchg_release
-#define xchg_release(ptr, ...) \
- __atomic_op_release(__typeof__(*ptr), xchg, ptr, __VA_ARGS__)
+#define xchg_release(...) __atomic_op_release(xchg, __VA_ARGS__)
#endif
#ifndef xchg
-#define xchg(ptr, ...) \
- __atomic_op_fence(__typeof__(*ptr), xchg, ptr, __VA_ARGS__)
+#define xchg(...) __atomic_op_fence(xchg, __VA_ARGS__)
#endif
#endif /* xchg_relaxed */
--
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