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Date: Wed, 15 Aug 2007 22:54:31 +0200
From: Sebastian Siewior <sebastian@breakpoint.cc>
To: linux-kernel@vger.kernel.org
Cc: Andi Kleen <ak@suse.de>, Chris Snook <csnook@redhat.com>
Subject: [patch 1/2] i386: use asm() like the other atomic operations already do.
Content-Disposition: inline; filename=atomic_i386.diff
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As Segher pointed out, inline asm is better than the volatile casting all over
the place. From the PowerPC patch description:
 Also use inline functions instead of macros; this actually
 improves code generation (some code becomes a little smaller,
 probably because of improved alias information -- just a few
 hundred bytes total on a default kernel build, nothing shocking).

My config with march=pentium-m and gcc (GCC) 4.1.2 (Gentoo 4.1.2):
  text    data     bss     dec     hex filename
  3434150  249176  176128 3859454  3ae3fe atomic_normal/vmlinux
  3435308  249176  176128 3860612  3ae884 atomic_inlineasm/vmlinux
  3436201  249176  176128 3861505  3aec01 atomic_inline_volatile/vmlinux
  3436203  249176  176128 3861507  3aec03 atomic_volatile/vmlinux

Signed-off-by: Sebastian Siewior <sebastian@breakpoint.cc>
Cc: Andi Kleen <ak@suse.de>
Cc: Chris Snook <csnook@redhat.com>
--- a/include/asm-i386/atomic.h
+++ b/include/asm-i386/atomic.h
@@ -25,7 +25,16 @@ typedef struct { int counter; } atomic_t
  * 
  * Atomically reads the value of @v.
  */ 
-#define atomic_read(v)		((v)->counter)
+static inline int atomic_read(const atomic_t *v)
+{
+	int t;
+
+	asm volatile(
+			"movl %1,%0"
+			: "=r"(t)
+			: "m"(v->counter));
+	return t;
+}
 
 /**
  * atomic_set - set atomic variable
@@ -34,7 +43,13 @@ typedef struct { int counter; } atomic_t
  * 
  * Atomically sets the value of @v to @i.
  */ 
-#define atomic_set(v,i)		(((v)->counter) = (i))
+static inline void atomic_set(atomic_t *v, int i)
+{
+	asm volatile(
+			"movl %1,%0"
+			: "=m"(v->counter)
+			: "ir"(i));
+}
 
 /**
  * atomic_add - add integer to atomic variable

--