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Commit 349c004e authored by Christoph Lameter's avatar Christoph Lameter Committed by Tejun Heo
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x86: A fast way to check capabilities of the current cpu 



Add this_cpu_has() which determines if the current cpu has a certain
ability using a segment prefix and a bit test operation.

For that we need to add bit operations to x86s percpu.h.

Many uses of cpu_has use a pointer passed to a function to determine
the current flags. That is no longer necessary after this patch.

However, this patch only converts the straightforward cases where
cpu_has is used with this_cpu_ptr. The rest is work for later.

-tj: Rolled up patch to add x86_ prefix and use percpu_read() instead
     of percpu_read_stable().

Signed-off-by: default avatarChristoph Lameter <cl@linux.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 89078d57

arch/x86/include/asm/cpufeature.h

+9 −4
Original line number Diff line number Diff line
@@ -207,8 +207,7 @@ extern const char * const x86_power_flags[32]; 
#define test_cpu_cap(c, bit)						\

	 test_bit(bit, (unsigned long *)((c)->x86_capability))



#define cpu_has(c, bit)							\

	(__builtin_constant_p(bit) &&					\

#define REQUIRED_MASK_BIT_SET(bit)					\

	 ( (((bit)>>5)==0 && (1UL<<((bit)&31) & REQUIRED_MASK0)) ||	\

	   (((bit)>>5)==1 && (1UL<<((bit)&31) & REQUIRED_MASK1)) ||	\

	   (((bit)>>5)==2 && (1UL<<((bit)&31) & REQUIRED_MASK2)) ||	\
@@ -218,10 +217,16 @@ extern const char * const x86_power_flags[32]; 
	   (((bit)>>5)==6 && (1UL<<((bit)&31) & REQUIRED_MASK6)) ||	\

	   (((bit)>>5)==7 && (1UL<<((bit)&31) & REQUIRED_MASK7)) ||	\

	   (((bit)>>5)==8 && (1UL<<((bit)&31) & REQUIRED_MASK8)) ||	\

	   (((bit)>>5)==9 && (1UL<<((bit)&31) & REQUIRED_MASK9)) )	\

	  ? 1 :								\

	   (((bit)>>5)==9 && (1UL<<((bit)&31) & REQUIRED_MASK9)) )



#define cpu_has(c, bit)							\

	(__builtin_constant_p(bit) && REQUIRED_MASK_BIT_SET(bit) ? 1 :	\

	 test_cpu_cap(c, bit))



#define this_cpu_has(bit)						\

	(__builtin_constant_p(bit) && REQUIRED_MASK_BIT_SET(bit) ? 1 : 	\

	 x86_this_cpu_test_bit(bit, (unsigned long *)&cpu_info.x86_capability))



#define boot_cpu_has(bit)	cpu_has(&boot_cpu_data, bit)



#define set_cpu_cap(c, bit)	set_bit(bit, (unsigned long *)((c)->x86_capability))

arch/x86/include/asm/percpu.h

+27 −0
Original line number Diff line number Diff line
@@ -542,6 +542,33 @@ do { \ 
	old__;								\

})



static __always_inline int x86_this_cpu_constant_test_bit(unsigned int nr,

                        const unsigned long __percpu *addr)

{

	unsigned long __percpu *a = (unsigned long *)addr + nr / BITS_PER_LONG;



	return ((1UL << (nr % BITS_PER_LONG)) & percpu_read(*a)) != 0;

}



static inline int x86_this_cpu_variable_test_bit(int nr,

                        const unsigned long __percpu *addr)

{

	int oldbit;



	asm volatile("bt "__percpu_arg(2)",%1\n\t"

			"sbb %0,%0"

			: "=r" (oldbit)

			: "m" (*(unsigned long *)addr), "Ir" (nr));



	return oldbit;

}



#define x86_this_cpu_test_bit(nr, addr)			\

	(__builtin_constant_p((nr))			\

	 ? x86_this_cpu_constant_test_bit((nr), (addr))	\

	 : x86_this_cpu_variable_test_bit((nr), (addr)))





#include <asm-generic/percpu.h>



/* We can use this directly for local CPU (faster). */

arch/x86/kernel/apic/apic.c

+1 −1
Original line number Diff line number Diff line
@@ -505,7 +505,7 @@ static void __cpuinit setup_APIC_timer(void) 
{

	struct clock_event_device *levt = &__get_cpu_var(lapic_events);



	if (cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_ARAT)) {

	if (this_cpu_has(X86_FEATURE_ARAT)) {

		lapic_clockevent.features &= ~CLOCK_EVT_FEAT_C3STOP;

		/* Make LAPIC timer preferrable over percpu HPET */

		lapic_clockevent.rating = 150;

arch/x86/kernel/process.c

+2 −2
Original line number Diff line number Diff line
@@ -449,7 +449,7 @@ EXPORT_SYMBOL_GPL(cpu_idle_wait); 
void mwait_idle_with_hints(unsigned long ax, unsigned long cx)

{

	if (!need_resched()) {

		if (cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_CLFLUSH_MONITOR))

		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))

			clflush((void *)&current_thread_info()->flags);



		__monitor((void *)&current_thread_info()->flags, 0, 0);
@@ -465,7 +465,7 @@ static void mwait_idle(void) 
	if (!need_resched()) {

		trace_power_start(POWER_CSTATE, 1, smp_processor_id());

		trace_cpu_idle(1, smp_processor_id());

		if (cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_CLFLUSH_MONITOR))

		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))

			clflush((void *)&current_thread_info()->flags);



		__monitor((void *)&current_thread_info()->flags, 0, 0);

arch/x86/kernel/smpboot.c

+2 −2
Original line number Diff line number Diff line
@@ -1332,9 +1332,9 @@ static inline void mwait_play_dead(void) 
	void *mwait_ptr;

	struct cpuinfo_x86 *c = __this_cpu_ptr(&cpu_info);



	if (!(cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)))

	if (!this_cpu_has(X86_FEATURE_MWAIT) && mwait_usable(c))

		return;

	if (!cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_CLFLSH))

	if (!this_cpu_has(X86_FEATURE_CLFLSH))

		return;

	if (__this_cpu_read(cpu_info.cpuid_level) < CPUID_MWAIT_LEAF)

		return;