From 4db7327194dba0cb91f274b0f606785a9ee5108d Mon Sep 17 00:00:00 2001
From: Kevin Hao <haokexin@gmail.com>
Date: Sat, 23 Jul 2016 14:42:41 +0530
Subject: [PATCH] powerpc: Add option to use jump label for cpu_has_feature()
We do binary patching of asm code using CPU features, which is a
one-time operation, done during early boot. However checks of CPU
features in C code are currently done at run time, even though the set
of CPU features can never change after boot.
We can optimise this by using jump labels to implement cpu_has_feature(),
meaning checks in C code are binary patched into a single nop or branch.
For a C sequence along the lines of:
if (cpu_has_feature(FOO))
return 2;
The generated code before is roughly:
ld r9,-27640(r2)
ld r9,0(r9)
lwz r9,32(r9)
cmpwi cr7,r9,0
bge cr7, 1f
li r3,2
blr
1: ...
After (true):
nop
li r3,2
blr
After (false):
b 1f
li r3,2
blr
1: ...
mpe: Rename MAX_CPU_FEATURES as we already have a #define with that
name, and define it simply as a constant, rather than doing tricks with
sizeof and NULL pointers. Rename the array to cpu_feature_keys. Use the
kconfig we added to guard it. Add BUILD_BUG_ON() if the feature is not a
compile time constant. Rewrite the change log.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/powerpc/include/asm/cpu_has_feature.h | 24 ++++++++++++++++++++++
arch/powerpc/include/asm/cputable.h | 6 ++++++
arch/powerpc/include/asm/mmu.h | 1 +
arch/powerpc/kernel/cputable.c | 20 ++++++++++++++++++
arch/powerpc/lib/feature-fixups.c | 1 +
5 files changed, 52 insertions(+)
diff --git a/arch/powerpc/include/asm/cpu_has_feature.h b/arch/powerpc/include/asm/cpu_has_feature.h
index c935c5854fed0..b9ce6425fdea0 100644
--- a/arch/powerpc/include/asm/cpu_has_feature.h
+++ b/arch/powerpc/include/asm/cpu_has_feature.h
@@ -11,10 +11,34 @@ static inline bool early_cpu_has_feature(unsigned long feature)
(CPU_FTRS_POSSIBLE & cur_cpu_spec->cpu_features & feature));
}
+#ifdef CONFIG_JUMP_LABEL_FEATURE_CHECKS
+#include <linux/jump_label.h>
+
+#define NUM_CPU_FTR_KEYS 64
+
+extern struct static_key_true cpu_feature_keys[NUM_CPU_FTR_KEYS];
+
+static __always_inline bool cpu_has_feature(unsigned long feature)
+{
+ int i;
+
+ BUILD_BUG_ON(!__builtin_constant_p(feature));
+
+ if (CPU_FTRS_ALWAYS & feature)
+ return true;
+
+ if (!(CPU_FTRS_POSSIBLE & feature))
+ return false;
+
+ i = __builtin_ctzl(feature);
+ return static_branch_likely(&cpu_feature_keys[i]);
+}
+#else
static inline bool cpu_has_feature(unsigned long feature)
{
return early_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 92961bcfbe3fb..82026b4193413 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -123,6 +123,12 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
extern const char *powerpc_base_platform;
+#ifdef CONFIG_JUMP_LABEL_FEATURE_CHECKS
+extern void cpu_feature_keys_init(void);
+#else
+static inline void cpu_feature_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 */
diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 08b4c06604d6f..37f55169df3ec 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -112,6 +112,7 @@
#define MMU_FTRS_PA6T MMU_FTRS_DEFAULT_HPTE_ARCH_V2 | \
MMU_FTR_CI_LARGE_PAGE | MMU_FTR_NO_SLBIE_B
#ifndef __ASSEMBLY__
+#include <linux/bug.h>
#include <asm/cputable.h>
#ifdef CONFIG_PPC_FSL_BOOK3E
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index d81f826d10296..e3da41f8ef939 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_FEATURE_CHECKS
+struct static_key_true cpu_feature_keys[NUM_CPU_FTR_KEYS] = {
+ [0 ... NUM_CPU_FTR_KEYS - 1] = STATIC_KEY_TRUE_INIT
+};
+EXPORT_SYMBOL_GPL(cpu_feature_keys);
+
+void __init cpu_feature_keys_init(void)
+{
+ int i;
+
+ for (i = 0; i < NUM_CPU_FTR_KEYS; i++) {
+ unsigned long f = 1ul << i;
+
+ if (!(cur_cpu_spec->cpu_features & f))
+ static_branch_disable(&cpu_feature_keys[i]);
+ }
+}
+#endif
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index ae57de78e2aa7..7a6ccbb74d915 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -195,6 +195,7 @@ void __init apply_feature_fixups(void)
* CPU/MMU features.
*/
jump_label_init();
+ cpu_feature_keys_init();
}
static int __init check_features(void)
--
2.30.2