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Subject[PATCH 3/4] perf, x86: Use ALTERNATIVE() to check for X86_FEATURE_PERFCTR_CORE
Date
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>
---
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)
--
1.7.3.4



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