x86: atomic64: Inline atomic64_read() again

Now atomic64_read() is light weight (no register pressure and
small icache), we can inline it again.

Also use "=&A" constraint instead of "+A" to avoid warning
about unitialized 'res' variable. (gcc had to force 0 in eax/edx)

  $ size vmlinux.prev vmlinux.after
     text    data     bss     dec     hex filename
  4908667  451676 1684868 7045211  6b805b vmlinux.prev
  4908651  451676 1684868 7045195  6b804b vmlinux.after

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
LKML-Reference: <4A4E1AA2.30002@gmail.com>
[ Also fix typo in atomic64_set() export ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 22 insertions, 0 deletions

diff --git a/arch/x86/include/asm/atomic_32.h b/arch/x86/include/asm/atomic_32.h
index d7c8849b8c67..dc5a667ff791 100644
--- a/arch/x86/include/asm/atomic_32.h
+++ b/arch/x86/include/asm/atomic_32.h
@@ -295,6 +295,28 @@ extern void atomic64_set(atomic64_t *ptr, u64 new_val);
  *
  * Atomically reads the value of @ptr and returns it.
  */
+static inline u64 atomic64_read(atomic64_t *ptr)
+{
+        u64 res;
+
+        /*
+         * Note, we inline this atomic64_t primitive because
+         * it only clobbers EAX/EDX and leaves the others
+         * untouched. We also (somewhat subtly) rely on the
+         * fact that cmpxchg8b returns the current 64-bit value
+         * of the memory location we are touching:
+         */
+        asm volatile(
+                "mov %%ebx, %%eax\n\t"
+                "mov %%ecx, %%edx\n\t"
+                LOCK_PREFIX "cmpxchg8b %1\n"
+                        : "=&A" (res)
+                        : "m" (*ptr)
+                );
+
+        return res;
+}
+
 extern u64 atomic64_read(atomic64_t *ptr);
 
 /**