Re: [PATCH 06/20] arch,avr32: Fold atomic_ops

[Peter Zijlstra <peterz@infradead.org>]

On Fri, May 09, 2014 at 10:51:55PM +0200, Peter Zijlstra wrote:
> On Fri, May 09, 2014 at 10:43:09PM +0200, Peter Zijlstra wrote:
> > On Fri, May 09, 2014 at 08:32:41PM +0200, Hans-Christian Egtvedt wrote:
> 
> > > > -	if (__builtin_constant_p(i) && (i >= -1048575) && (i <= 1048576))
> > > > -		result = atomic_sub_return(-i, v);
> > > 
> > > I do not recall why we did it like this any more, I would assume both sub and
> > > add to be single cycle instructions.
> 
> Similarly, can I rip out atomic_sub_unless() ?

Something like so?

---
Subject: arch,avr32: Fold atomic_ops
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Apr 9 21:51:29 CEST 2014

Many of the atomic op implementations are the same except for one
instruction; fold the lot into a few CPP macros and reduce LoC.

This also prepares for easy addition of new ops.

Requires the asm_op because of eor.

The avr32 sub instruction is limited to 21 bits, Hans-Christian cannot
recall the reason for the weird __builtin_constant_p() tests so take all
that out and use a straight fwd negate add instead of subtract.

Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 arch/avr32/include/asm/atomic.h |  145 +++++++++++++++-------------------------
 1 file changed, 55 insertions(+), 90 deletions(-)

--- a/arch/avr32/include/asm/atomic.h
+++ b/arch/avr32/include/asm/atomic.h
@@ -22,117 +22,84 @@
 #define atomic_read(v)		(*(volatile int *)&(v)->counter)
 #define atomic_set(v, i)	(((v)->counter) = i)
 
-/*
- * atomic_sub_return - subtract the atomic variable
- * @i: integer value to subtract
- * @v: pointer of type atomic_t
- *
- * Atomically subtracts @i from @v. Returns the resulting value.
- */
-static inline int atomic_sub_return(int i, atomic_t *v)
-{
-	int result;
-
-	asm volatile(
-		"/* atomic_sub_return */\n"
-		"1:	ssrf	5\n"
-		"	ld.w	%0, %2\n"
-		"	sub	%0, %3\n"
-		"	stcond	%1, %0\n"
-		"	brne	1b"
-		: "=&r"(result), "=o"(v->counter)
-		: "m"(v->counter), "rKs21"(i)
-		: "cc");
-
-	return result;
+#define ATOMIC_OP(op, asm_op)						\
+static inline void atomic_##op(int i, atomic_t *v)			\
+{									\
+	int result;							\
+									\
+	asm volatile(							\
+		"/* atomic_" #op " */\n"				\
+		"1:	ssrf	5\n"					\
+		"	ld.w	%0, %2\n"				\
+		"	" #asm_op "	%0, %3\n"			\
+		"	stcond	%1, %0\n"				\
+		"	brne	1b"					\
+		: "=&r"(result), "=o"(v->counter)			\
+		: "m"(v->counter), "r"(i)				\
+		: "cc");						\
+}									\
+
+#define ATOMIC_OP_RETURN(op, asm_op)					\
+static inline int atomic_##op##_return(int i, atomic_t *v)		\
+{									\
+	int result;							\
+									\
+	asm volatile(							\
+		"/* atomic_" #op "_return */\n"				\
+		"1:	ssrf	5\n"					\
+		"	ld.w	%0, %2\n"				\
+		"	" #asm_op "	%0, %3\n"			\
+		"	stcond	%1, %0\n"				\
+		"	brne	1b"					\
+		: "=&r"(result), "=o"(v->counter)			\
+		: "m"(v->counter), "r"(i)				\
+		: "cc");						\
+									\
+	return result;							\
 }
 
+#define ATOMIC_OPS(op, asm_op)						\
+	ATOMIC_OP(op, asm_op)						\
+	ATOMIC_OP_RETURN(op, asm_op)
+
+ATOMIC_OPS(add, add)
+
+#undef ATOMIC_OPS
+#undef ATOMIC_OP_RETURN
+#undef ATOMIC_OP
+
 /*
- * atomic_add_return - add integer to atomic variable
- * @i: integer value to add
- * @v: pointer of type atomic_t
- *
- * Atomically adds @i to @v. Returns the resulting value.
+ * The 'sub' instruction is limited to 21 bits, use negate add instead.
  */
-static inline int atomic_add_return(int i, atomic_t *v)
-{
-	int result;
-
-	if (__builtin_constant_p(i) && (i >= -1048575) && (i <= 1048576))
-		result = atomic_sub_return(-i, v);
-	else
-		asm volatile(
-			"/* atomic_add_return */\n"
-			"1:	ssrf	5\n"
-			"	ld.w	%0, %1\n"
-			"	add	%0, %3\n"
-			"	stcond	%2, %0\n"
-			"	brne	1b"
-			: "=&r"(result), "=o"(v->counter)
-			: "m"(v->counter), "r"(i)
-			: "cc", "memory");
-
-	return result;
-}
+#define atomic_sub(i, v)	atomic_add(-(i), (v))
+#define atomic_sub_return(i, v)	atomic_add_return(-(i), (v))
 
 /*
- * atomic_sub_unless - sub unless the number is a given value
+ * __atomic_add_unless - add unless the number is a given value
  * @v: pointer of type atomic_t
- * @a: the amount to subtract from v...
+ * @a: the amount to add to v...
  * @u: ...unless v is equal to u.
  *
- * Atomically subtract @a from @v, so long as it was not @u.
+ * Atomically adds @a to @v, so long as it was not @u.
  * Returns the old value of @v.
 */
-static inline void atomic_sub_unless(atomic_t *v, int a, int u)
+static inline int __atomic_add_unless(atomic_t *v, int a, int u)
 {
-	int tmp;
+	int tmp, old = atomic_read(v);
 
 	asm volatile(
-		"/* atomic_sub_unless */\n"
+		"/* __atomic_add_unless */\n"
 		"1:	ssrf	5\n"
 		"	ld.w	%0, %2\n"
 		"	cp.w	%0, %4\n"
 		"	breq	1f\n"
-		"	sub	%0, %3\n"
+		"	add	%0, %3\n"
 		"	stcond	%1, %0\n"
 		"	brne	1b\n"
 		"1:"
 		: "=&r"(tmp), "=o"(v->counter)
-		: "m"(v->counter), "rKs21"(a), "rKs21"(u)
+		: "m"(v->counter), "r"(a), "ir"(u)
 		: "cc", "memory");
-}
-
-/*
- * __atomic_add_unless - add unless the number is a given value
- * @v: pointer of type atomic_t
- * @a: the amount to add to v...
- * @u: ...unless v is equal to u.
- *
- * Atomically adds @a to @v, so long as it was not @u.
- * Returns the old value of @v.
-*/
-static inline int __atomic_add_unless(atomic_t *v, int a, int u)
-{
-	int tmp, old = atomic_read(v);
-
-	if (__builtin_constant_p(a) && (a >= -1048575) && (a <= 1048576))
-		atomic_sub_unless(v, -a, u);
-	else {
-		asm volatile(
-			"/* __atomic_add_unless */\n"
-			"1:	ssrf	5\n"
-			"	ld.w	%0, %2\n"
-			"	cp.w	%0, %4\n"
-			"	breq	1f\n"
-			"	add	%0, %3\n"
-			"	stcond	%1, %0\n"
-			"	brne	1b\n"
-			"1:"
-			: "=&r"(tmp), "=o"(v->counter)
-			: "m"(v->counter), "r"(a), "ir"(u)
-			: "cc", "memory");
-	}
 
 	return old;
 }
@@ -168,8 +135,6 @@ static inline int atomic_sub_if_positive
 #define atomic_xchg(v, new)	(xchg(&((v)->counter), new))
 #define atomic_cmpxchg(v, o, n)	(cmpxchg(&((v)->counter), (o), (n)))
 
-#define atomic_sub(i, v)	(void)atomic_sub_return(i, v)
-#define atomic_add(i, v)	(void)atomic_add_return(i, v)
 #define atomic_dec(v)		atomic_sub(1, (v))
 #define atomic_inc(v)		atomic_add(1, (v))