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Commit 4db73271 authored by Kevin Hao's avatar Kevin Hao Committed by Michael Ellerman
Browse files

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: default avatarKevin Hao <haokexin@gmail.com>
Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent bfbfc8a4

arch/powerpc/include/asm/cpu_has_feature.h

+24 −0
Original line number Diff line number Diff line
@@ -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 */

arch/powerpc/include/asm/cputable.h

+6 −0
Original line number Diff line number Diff line
@@ -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 */

arch/powerpc/include/asm/mmu.h

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/powerpc/kernel/cputable.c

+20 −0
Original line number Diff line number Diff line
@@ -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

arch/powerpc/lib/feature-fixups.c

+1 −0
Original line number Diff line number Diff line
@@ -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)