[PATCH 4/5] powerpc: use the jump label for cpu_has_feature

[Kevin Hao]

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. But we can only use
the jump label for this check only after the execution of
jump_label_init(), so we introduce another jump label to
still do the feature check by default before all the cpu
feature jump labels are initialized.

Signed-off-by: Kevin Hao <haokexin at gmail.com>
---
 arch/powerpc/include/asm/cpufeatures.h | 28 ++++++++++++++++++++++++++++
 arch/powerpc/kernel/cputable.c         | 23 +++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/arch/powerpc/include/asm/cpufeatures.h b/arch/powerpc/include/asm/cpufeatures.h
index 37650db..598ac91 100644
--- a/arch/powerpc/include/asm/cpufeatures.h
+++ b/arch/powerpc/include/asm/cpufeatures.h
@@ -2,7 +2,34 @@
 #define __ASM_POWERPC_CPUFEATURES_H
 
 #include <asm/cputable.h>
+#ifdef CONFIG_JUMP_LABEL
+#include <linux/atomic.h>
+#include <linux/jump_label_base.h>
 
+#ifdef __powerpc64__
+#define MAX_CPU_FEATURES	64
+#else
+#define MAX_CPU_FEATURES	32
+#endif
+extern struct static_key cpu_feat_keys[MAX_CPU_FEATURES];
+extern struct static_key cpu_feat_keys_enabled;
+
+static inline int cpu_has_feature(unsigned long feature)
+{
+	if (CPU_FTRS_ALWAYS & feature)
+		return 1;
+
+	if (!(CPU_FTRS_POSSIBLE | feature))
+		return 0;
+
+	if (static_key_false(&cpu_feat_keys_enabled)) {
+		int i = __builtin_ctzl(feature);
+
+		return static_key_false(&cpu_feat_keys[i]);
+	} else
+		return !!(cur_cpu_spec->cpu_features & feature);
+}
+#else
 static inline int cpu_has_feature(unsigned long feature)
 {
 	return (CPU_FTRS_ALWAYS & feature) ||
@@ -10,5 +37,6 @@ static inline int cpu_has_feature(unsigned long feature)
 		& cur_cpu_spec->cpu_features
 		& feature);
 }
+#endif
 
 #endif /* __ASM_POWERPC_CPUFEATURE_H */
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index 22973a7..2014ab7 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -21,6 +21,7 @@
 #include <asm/prom.h>		/* for PTRRELOC on ARCH=ppc */
 #include <asm/mmu.h>
 #include <asm/setup.h>
+#include <asm/cpufeatures.h>
 
 struct cpu_spec* cur_cpu_spec = NULL;
 EXPORT_SYMBOL(cur_cpu_spec);
@@ -2258,3 +2259,25 @@ struct cpu_spec * __init identify_cpu(unsigned long offset, unsigned int pvr)
 
 	return NULL;
 }
+
+#ifdef CONFIG_JUMP_LABEL
+struct static_key cpu_feat_keys[MAX_CPU_FEATURES];
+struct static_key cpu_feat_keys_enabled;
+
+static __init int cpu_feat_keys_init(void)
+{
+	int i;
+
+	for (i = 0; i < MAX_CPU_FEATURES; i++) {
+		unsigned long f = 1 << i;
+
+		if (cur_cpu_spec->cpu_features & f)
+			static_key_slow_inc(&cpu_feat_keys[i]);
+	}
+
+	static_key_slow_inc(&cpu_feat_keys_enabled);
+
+	return 0;
+}
+early_initcall(cpu_feat_keys_init);
+#endif
-- 
1.8.3.1