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

[pandora-kernel.git] / arch / x86 / include / asm / percpu.h

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index a18c038..b65a36d 100644 (file)
--- 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)