From: Kevin Hao <haoke...@gmail.com>
The mmu features are fixed once the probe of mmu features are done.
And the function mmu_has_feature() does be used in some hot path.
The checking of the mmu features for each time of invoking of
mmu_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 (mmu_has_feature(MMU_FTR_XXX))
xxx()
Before:
lis r9,-16230
lwz r9,12324(r9)
lwz r9,24(r9)
andi. r10,r9,16
beqlr+
After:
nop if MMU_FTR_XXX is enabled
b xxx if MMU_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/mmu.h | 36 ++++++++++++++++++++++++++++++++++++
arch/powerpc/kernel/cputable.c | 17 +++++++++++++++++
arch/powerpc/kernel/setup_32.c | 1 +
arch/powerpc/kernel/setup_64.c | 1 +
4 files changed, 55 insertions(+)
diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index c488db09f7a0..e453e095579e 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -143,6 +143,41 @@ static inline bool __mmu_has_feature(unsigned long feature)
return !!(MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
}
+#ifdef CONFIG_JUMP_LABEL
+#include <linux/jump_label.h>
+
+#define MAX_MMU_FEATURES (8 * sizeof(((struct cpu_spec
*)0)->mmu_features))
+
+extern struct static_key_true mmu_feat_keys[MAX_MMU_FEATURES];
+
+extern void mmu_feat_keys_init(void);
+
+static __always_inline bool mmu_has_feature(unsigned long feature)
+{
+ int i;
+
+ if (!(MMU_FTRS_POSSIBLE & feature))
+ return false;
+
+ i = __builtin_ctzl(feature);
+ return static_branch_likely(&mmu_feat_keys[i]);
+}
+
+static inline void mmu_clear_feature(unsigned long feature)
+{
+ int i;
+
+ i = __builtin_ctzl(feature);
+ cur_cpu_spec->mmu_features &= ~feature;
+ static_branch_disable(&mmu_feat_keys[i]);
+}
+#else
+
+static inline void mmu_feat_keys_init(void)
+{
+
+}
+
static inline bool mmu_has_feature(unsigned long feature)
{
return __mmu_has_feature(feature);
@@ -152,6 +187,7 @@ static inline void mmu_clear_feature(unsigned long feature)
{
cur_cpu_spec->mmu_features &= ~feature;
}
+#endif /* CONFIG_JUMP_LABEL */
extern unsigned int __start___mmu_ftr_fixup, __stop___mmu_ftr_fixup;
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index b0a24b425441..a98630183e92 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -2243,4 +2243,21 @@ void __init cpu_feat_keys_init(void)
static_branch_disable(&cpu_feat_keys[i]);
}
}
+
+struct static_key_true mmu_feat_keys[MAX_MMU_FEATURES] = {
+ [0 ... MAX_MMU_FEATURES - 1] = STATIC_KEY_TRUE_INIT
+};
+EXPORT_SYMBOL_GPL(mmu_feat_keys);
+
+void __init mmu_feat_keys_init(void)
+{
+ int i;
+
+ for (i = 0; i < MAX_MMU_FEATURES; i++) {
+ unsigned long f = 1ul << i;
+
+ if (!(cur_cpu_spec->mmu_features & f))
+ static_branch_disable(&mmu_feat_keys[i]);
+ }
+}
#endif
diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
index ac5b41ad94ed..cd0d8814bd9b 100644
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -107,6 +107,7 @@ notrace unsigned long __init early_init(unsigned long
dt_ptr)
*/
jump_label_init();
cpu_feat_keys_init();
+ mmu_feat_keys_init();
return KERNELBASE + offset;
}
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 1bd0d19afe1d..8222950f820f 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -487,6 +487,7 @@ void __init setup_system(void)
*/
jump_label_init();
cpu_feat_keys_init();
+ mmu_feat_keys_init();
/*
* Unflatten the device-tree passed by prom_init or kexec
--
2.7.4
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