Messages in this thread Patch in this message |  | | | Date | Wed, 15 Dec 2010 14:07:39 -0600 (CST) | | From | Christoph Lameter <> | | Subject | x86: A fast way to check capabilities of the current cpu |
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Subject: 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.
Signed-off-by: Christoph Lameter <cl@linux.com>
--- arch/x86/include/asm/cpufeature.h | 13 +++++++++---- arch/x86/include/asm/percpu.h | 27 +++++++++++++++++++++++++++ arch/x86/kernel/apic/apic.c | 2 +- arch/x86/kernel/process.c | 4 ++-- arch/x86/kernel/smpboot.c | 4 ++-- 5 files changed, 41 insertions(+), 9 deletions(-) Index: linux-2.6/arch/x86/include/asm/cpufeature.h =================================================================== --- linux-2.6.orig/arch/x86/include/asm/cpufeature.h 2010-12-15 12:38:52.000000000 -0600 +++ linux-2.6/arch/x86/include/asm/cpufeature.h 2010-12-15 12:54:48.000000000 -0600 @@ -206,8 +206,7 @@ extern const char * const x86_power_flag #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)) || \ @@ -217,10 +216,16 @@ extern const char * const x86_power_flag (((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 : \ + 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)) Index: linux-2.6/arch/x86/kernel/apic/apic.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/apic/apic.c 2010-12-15 12:38:52.000000000 -0600 +++ linux-2.6/arch/x86/kernel/apic/apic.c 2010-12-15 12:38:53.000000000 -0600 @@ -516,7 +516,7 @@ static void __cpuinit setup_APIC_timer(v { 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; Index: linux-2.6/arch/x86/include/asm/percpu.h =================================================================== --- linux-2.6.orig/arch/x86/include/asm/percpu.h 2010-12-15 12:38:52.000000000 -0600 +++ linux-2.6/arch/x86/include/asm/percpu.h 2010-12-15 13:06:27.000000000 -0600 @@ -545,6 +545,33 @@ do { \ old__; \ })
+static __always_inline int 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_stable(*a)) != 0; +} + +static inline int 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 this_cpu_test_bit(nr, addr) \ + (__builtin_constant_p((nr)) \ + ? this_cpu_constant_test_bit((nr), (addr)) \ + : this_cpu_variable_test_bit((nr), (addr))) + + #include <asm-generic/percpu.h>
/* We can use this directly for local CPU (faster). */ Index: linux-2.6/arch/x86/kernel/process.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/process.c 2010-12-15 12:38:52.000000000 -0600 +++ linux-2.6/arch/x86/kernel/process.c 2010-12-15 12:38:53.000000000 -0600 @@ -445,7 +445,7 @@ void mwait_idle_with_hints(unsigned long { trace_power_start(POWER_CSTATE, (ax>>4)+1, smp_processor_id()); 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 *)¤t_thread_info()->flags);
__monitor((void *)¤t_thread_info()->flags, 0, 0); @@ -460,7 +460,7 @@ static void mwait_idle(void) { if (!need_resched()) { trace_power_start(POWER_CSTATE, 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 *)¤t_thread_info()->flags);
__monitor((void *)¤t_thread_info()->flags, 0, 0); Index: linux-2.6/arch/x86/kernel/smpboot.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/smpboot.c 2010-12-15 12:38:52.000000000 -0600 +++ linux-2.6/arch/x86/kernel/smpboot.c 2010-12-15 12:38:53.000000000 -0600 @@ -1397,9 +1397,9 @@ static inline void mwait_play_dead(void) int i; void *mwait_ptr;
- if (!cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_MWAIT)) + if (!this_cpu_has(X86_FEATURE_MWAIT)) 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;
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