[Xen-changelog] [xen-unstable] x86: optimize this_cpu()

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1279041448 -3600
# Node ID d867eb643fe4d9e5ee95fac945df5971dadd345c
# Parent  f72879804eb083dec369f450d35ba8a16a1ad020
x86: optimize this_cpu()

Besides the .text space savings of over 2.5k on x86-64 (1.5k for
x86-32) this removes a load (plus a lea on x86-64) from various
frequently executed code paths, and finally provides a reason (other
than legibility) to prefer this_cpu() over per_cpu() in all places
where smp_processor_id() isn't being called anyway.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
---
 xen/include/asm-x86/current.h |   13 ++++++++++---
 xen/include/asm-x86/percpu.h  |    2 +-
 2 files changed, 11 insertions(+), 4 deletions(-)

diff -r f72879804eb0 -r d867eb643fe4 xen/include/asm-x86/current.h
--- a/xen/include/asm-x86/current.h     Tue Jul 13 18:13:33 2010 +0100
+++ b/xen/include/asm-x86/current.h     Tue Jul 13 18:17:28 2010 +0100
@@ -16,8 +16,12 @@ struct vcpu;
 
 struct cpu_info {
     struct cpu_user_regs guest_cpu_user_regs;
-    unsigned int         processor_id;
-    struct vcpu         *current_vcpu;
+    unsigned int processor_id;
+    struct vcpu *current_vcpu;
+    unsigned long per_cpu_offset;
+#ifdef __x86_64__ /* get_stack_bottom() must be 16-byte aligned */
+    unsigned long __pad_for_stack_bottom;
+#endif
 };
 
 static inline struct cpu_info *get_cpu_info(void)
@@ -35,7 +39,10 @@ static inline struct cpu_info *get_cpu_i
 #define current               (get_current())
 
 #define get_processor_id()    (get_cpu_info()->processor_id)
-#define set_processor_id(id)  (get_cpu_info()->processor_id = (id))
+#define set_processor_id(id)  do {                                      \
+    struct cpu_info *ci__ = get_cpu_info();                             \
+    ci__->per_cpu_offset = __per_cpu_offset[ci__->processor_id = (id)]; \
+} while (0)
 
 #define guest_cpu_user_regs() (&get_cpu_info()->guest_cpu_user_regs)
 
diff -r f72879804eb0 -r d867eb643fe4 xen/include/asm-x86/percpu.h
--- a/xen/include/asm-x86/percpu.h      Tue Jul 13 18:13:33 2010 +0100
+++ b/xen/include/asm-x86/percpu.h      Tue Jul 13 18:17:28 2010 +0100
@@ -16,7 +16,7 @@ void percpu_init_areas(void);
 #define per_cpu(var, cpu)  \
     (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]))
 #define __get_cpu_var(var) \
-    (per_cpu(var, smp_processor_id()))
+    (*RELOC_HIDE(&per_cpu__##var, get_cpu_info()->per_cpu_offset))
 
 #define DECLARE_PER_CPU(type, name) extern __typeof__(type) per_cpu__##name
 

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