From: Kevin Hao <haoke...@gmail.com>
The cpu features are fixed once the probe of cpu features are done.
And the function cpu_has_feature() does be used in some hot path.
The checking of the cpu features for each time of invoking of
cpu_has_feature() seems suboptimal. This tries to reduce this
overhead of this check by using jump label.
The generated assemble code of the following c program:
if (cpu_has_feature(CPU_FTR_XXX))
xxx()
Before:
lis r9,-16230
lwz r9,12324(r9)
lwz r9,12(r9)
andi. r10,r9,512
beqlr-
After:
nop if CPU_FTR_XXX is enabled
b xxx if CPU_FTR_XXX is not enabled
Signed-off-by: Kevin Hao <haoke...@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
---
arch/powerpc/include/asm/cpufeatures.h | 21 +++++++++++++++++++++
arch/powerpc/include/asm/cputable.h | 8 ++++++++
arch/powerpc/kernel/cputable.c | 20 ++++++++++++++++++++
arch/powerpc/kernel/setup_32.c | 1 +
arch/powerpc/kernel/setup_64.c | 1 +
5 files changed, 51 insertions(+)
diff --git a/arch/powerpc/include/asm/cpufeatures.h
b/arch/powerpc/include/asm/cpufeatures.h
index bfa6cb8f5629..4a4a0b898463 100644
--- a/arch/powerpc/include/asm/cpufeatures.h
+++ b/arch/powerpc/include/asm/cpufeatures.h
@@ -13,10 +13,31 @@ static inline bool __cpu_has_feature(unsigned long feature)
return !!(CPU_FTRS_POSSIBLE & cur_cpu_spec->cpu_features & feature);
}
+#ifdef CONFIG_JUMP_LABEL
+#include <linux/jump_label.h>
+
+extern struct static_key_true cpu_feat_keys[MAX_CPU_FEATURES];
+
+static __always_inline bool cpu_has_feature(unsigned long feature)
+{
+ int i;
+
+ if (CPU_FTRS_ALWAYS & feature)
+ return true;
+
+ if (!(CPU_FTRS_POSSIBLE & feature))
+ return false;
+
+ i = __builtin_ctzl(feature);
+ return static_branch_likely(&cpu_feat_keys[i]);
+}
+#else
static inline bool cpu_has_feature(unsigned long feature)
{
return __cpu_has_feature(feature);
}
+#endif
+
#endif /* __ASSEMBLY__ */
#endif /* __ASM_POWERPC_CPUFEATURE_H */
diff --git a/arch/powerpc/include/asm/cputable.h
b/arch/powerpc/include/asm/cputable.h
index a49ea95849f8..6c161e456759 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -122,6 +122,12 @@ extern void do_feature_fixups(unsigned long value, void
*fixup_start,
extern const char *powerpc_base_platform;
+#ifdef CONFIG_JUMP_LABEL
+extern void cpu_feat_keys_init(void);
+#else
+static inline void cpu_feat_keys_init(void) { }
+#endif
+
/* TLB flush actions. Used as argument to cpu_spec.flush_tlb() hook */
enum {
TLB_INVAL_SCOPE_GLOBAL = 0, /* invalidate all TLBs */
@@ -132,6 +138,8 @@ enum {
/* CPU kernel features */
+#define MAX_CPU_FEATURES (8 * sizeof(((struct cpu_spec
*)0)->cpu_features))
+
/* Retain the 32b definitions all use bottom half of word */
#define CPU_FTR_COHERENT_ICACHE ASM_CONST(0x00000001)
#define CPU_FTR_L2CR ASM_CONST(0x00000002)
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index d81f826d1029..67ce4816998e 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -15,6 +15,7 @@
#include <linux/threads.h>
#include <linux/init.h>
#include <linux/export.h>
+#include <linux/jump_label.h>
#include <asm/oprofile_impl.h>
#include <asm/cputable.h>
@@ -2224,3 +2225,22 @@ struct cpu_spec * __init identify_cpu(unsigned long
offset, unsigned int pvr)
return NULL;
}
+
+#ifdef CONFIG_JUMP_LABEL
+struct static_key_true cpu_feat_keys[MAX_CPU_FEATURES] = {
+ [0 ... MAX_CPU_FEATURES - 1] = STATIC_KEY_TRUE_INIT
+};
+EXPORT_SYMBOL_GPL(cpu_feat_keys);
+
+void __init cpu_feat_keys_init(void)
+{
+ int i;
+
+ for (i = 0; i < MAX_CPU_FEATURES; i++) {
+ unsigned long f = 1ul << i;
+
+ if (!(cur_cpu_spec->cpu_features & f))
+ static_branch_disable(&cpu_feat_keys[i]);
+ }
+}
+#endif
diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
index ccac1cfd877d..ac5b41ad94ed 100644
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -106,6 +106,7 @@ notrace unsigned long __init early_init(unsigned long
dt_ptr)
* by now.
*/
jump_label_init();
+ cpu_feat_keys_init();
return KERNELBASE + offset;
}
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index c6f6cbcbee91..ab7710e369c1 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -486,6 +486,7 @@ void __init setup_system(void)
* by now.
*/
jump_label_init();
+ cpu_feat_keys_init();
/*
* Unflatten the device-tree passed by prom_init or kexec
--
2.7.4
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