From 4db7327194dba0cb91f274b0f606785a9ee5108d Mon Sep 17 00:00:00 2001 From: Kevin Hao Date: Sat, 23 Jul 2016 14:42:41 +0530 Subject: 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 Signed-off-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/cputable.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'arch/powerpc/kernel') diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c index d81f826d1029..e3da41f8ef93 100644 --- a/arch/powerpc/kernel/cputable.c +++ b/arch/powerpc/kernel/cputable.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include @@ -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 -- cgit v1.2.3