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

From: Peter Zijlstra
Date: Fri May 09 2014 - 17:17:43 EST

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@xxxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Haavard Skinnemoen <hskinnemoen@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
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))

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