[tip:perf/core] perf, x86: Use ALTERNATIVE() to check for X86_FEATURE_PERFCTR_CORE

[tip-bot for Robert Richter <robert.richter@amd.com>]

Commit-ID:  c8e5910edf8bbe2e5c6c35a4ef2a578cc7893b25
Gitweb:     http://git.kernel.org/tip/c8e5910edf8bbe2e5c6c35a4ef2a578cc7893b25
Author:     Robert Richter <robert.richter@amd.com>
AuthorDate: Sat, 16 Apr 2011 02:27:55 +0200
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 19 Apr 2011 10:08:12 +0200

perf, x86: Use ALTERNATIVE() to check for X86_FEATURE_PERFCTR_CORE

Using ALTERNATIVE() when checking for X86_FEATURE_PERFCTR_CORE avoids
an extra pointer chase and data cache hit.

Signed-off-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1302913676-14352-4-git-send-email-robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/cpu/perf_event.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index eed3673a..224a84f 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -31,6 +31,7 @@
 #include <asm/nmi.h>
 #include <asm/compat.h>
 #include <asm/smp.h>
+#include <asm/alternative.h>
 
 #if 0
 #undef wrmsrl
@@ -363,12 +364,18 @@ again:
 	return new_raw_count;
 }
 
-/* using X86_FEATURE_PERFCTR_CORE to later implement ALTERNATIVE() here */
 static inline int x86_pmu_addr_offset(int index)
 {
-	if (boot_cpu_has(X86_FEATURE_PERFCTR_CORE))
-		return index << 1;
-	return index;
+	int offset;
+
+	/* offset = X86_FEATURE_PERFCTR_CORE ? index << 1 : index */
+	alternative_io(ASM_NOP2,
+		       "shll $1, %%eax",
+		       X86_FEATURE_PERFCTR_CORE,
+		       "=a" (offset),
+		       "a"  (index));
+
+	return offset;
 }
 
 static inline unsigned int x86_pmu_config_addr(int index)