Merge branch 'x86-percpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'x86-percpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86, percpu: Collect hot percpu variables into one cacheline
  x86, percpu: Fix DECLARE/DEFINE_PER_CPU_PAGE_ALIGNED()
  x86, percpu: Add 'percpu_read_stable()' interface for cacheable accesses

1 files changed, 19 insertions, 7 deletions

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 103f1ddb0d85..04eacefcfd26 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -49,7 +49,7 @@
 #define __percpu_arg(x)		"%%"__stringify(__percpu_seg)":%P" #x
 #define __my_cpu_offset		percpu_read(this_cpu_off)
 #else
-#define __percpu_arg(x)		"%" #x
+#define __percpu_arg(x)		"%P" #x
 #endif
 
 /*
@@ -104,36 +104,48 @@ do {							\
 	}						\
 } while (0)
 
-#define percpu_from_op(op, var)				\
+#define percpu_from_op(op, var, constraint)		\
 ({							\
 	typeof(var) ret__;				\
 	switch (sizeof(var)) {				\
 	case 1:						\
 		asm(op "b "__percpu_arg(1)",%0"		\
 		    : "=q" (ret__)			\
-		    : "m" (var));			\
+		    : constraint);			\
 		break;					\
 	case 2:						\
 		asm(op "w "__percpu_arg(1)",%0"		\
 		    : "=r" (ret__)			\
-		    : "m" (var));			\
+		    : constraint);			\
 		break;					\
 	case 4:						\
 		asm(op "l "__percpu_arg(1)",%0"		\
 		    : "=r" (ret__)			\
-		    : "m" (var));			\
+		    : constraint);			\
 		break;					\
 	case 8:						\
 		asm(op "q "__percpu_arg(1)",%0"		\
 		    : "=r" (ret__)			\
-		    : "m" (var));			\
+		    : constraint);			\
 		break;					\
 	default: __bad_percpu_size();			\
 	}						\
 	ret__;						\
 })
 
-#define percpu_read(var)	percpu_from_op("mov", per_cpu__##var)
+/*
+ * percpu_read() makes gcc load the percpu variable every time it is
+ * accessed while percpu_read_stable() allows the value to be cached.
+ * percpu_read_stable() is more efficient and can be used if its value
+ * is guaranteed to be valid across cpus.  The current users include
+ * get_current() and get_thread_info() both of which are actually
+ * per-thread variables implemented as per-cpu variables and thus
+ * stable for the duration of the respective task.
+ */
+#define percpu_read(var)	percpu_from_op("mov", per_cpu__##var,	\
+					       "m" (per_cpu__##var))
+#define percpu_read_stable(var)	percpu_from_op("mov", per_cpu__##var,	\
+					       "p" (&per_cpu__##var))
 #define percpu_write(var, val)	percpu_to_op("mov", per_cpu__##var, val)
 #define percpu_add(var, val)	percpu_to_op("add", per_cpu__##var, val)
 #define percpu_sub(var, val)	percpu_to_op("sub", per_cpu__##var, val)