Messages in this thread Patch in this message | | | Date | Mon, 24 Jan 2011 18:23:57 +0100 | From | Tejun Heo <> | Subject | [PATCH 1/3] x86: A fast way to check capabilities of the current cpu |
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From: Christoph Lameter <cl@linux.com>
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: Christoph Lameter <cl@linux.com> Acked-by: Tejun Heo <tj@kernel.org> --- hpa, I think it's better to route these three patches through x86 tree rather than percpu. Can you please take these?
Thanks.
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: work/arch/x86/include/asm/cpufeature.h =================================================================== --- work.orig/arch/x86/include/asm/cpufeature.h +++ work/arch/x86/include/asm/cpufeature.h @@ -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 : \ + 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)) Index: work/arch/x86/kernel/apic/apic.c =================================================================== --- work.orig/arch/x86/kernel/apic/apic.c +++ work/arch/x86/kernel/apic/apic.c @@ -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: work/arch/x86/include/asm/percpu.h =================================================================== --- work.orig/arch/x86/include/asm/percpu.h +++ work/arch/x86/include/asm/percpu.h @@ -492,6 +492,33 @@ 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). */ Index: work/arch/x86/kernel/process.c =================================================================== --- work.orig/arch/x86/kernel/process.c +++ work/arch/x86/kernel/process.c @@ -441,7 +441,7 @@ 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 *)¤t_thread_info()->flags); __monitor((void *)¤t_thread_info()->flags, 0, 0); @@ -457,7 +457,7 @@ 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 *)¤t_thread_info()->flags); __monitor((void *)¤t_thread_info()->flags, 0, 0); Index: work/arch/x86/kernel/smpboot.c =================================================================== --- work.orig/arch/x86/kernel/smpboot.c +++ work/arch/x86/kernel/smpboot.c @@ -1403,9 +1403,9 @@ 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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