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Subject[x86 this_cpu_has V1 1/4] 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 2011-03-11 08:41:12.000000000 -0600
+++ linux-2.6/arch/x86/include/asm/cpufeature.h 2011-03-11 10:18:06.000000000 -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 : \
+ 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: linux-2.6/arch/x86/kernel/apic/apic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/apic/apic.c 2011-03-11 08:41:12.000000000 -0600
+++ linux-2.6/arch/x86/kernel/apic/apic.c 2011-03-11 09:29:46.000000000 -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 2011-03-11 08:41:12.000000000 -0600
+++ linux-2.6/arch/x86/include/asm/percpu.h 2011-03-11 10:18:06.000000000 -0600
@@ -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: linux-2.6/arch/x86/kernel/process.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/process.c 2011-03-11 08:41:12.000000000 -0600
+++ linux-2.6/arch/x86/kernel/process.c 2011-03-11 09:29:46.000000000 -0600
@@ -452,7 +452,7 @@ 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);
@@ -468,7 +468,7 @@ 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);
Index: linux-2.6/arch/x86/kernel/smpboot.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/smpboot.c 2011-03-11 08:41:12.000000000 -0600
+++ linux-2.6/arch/x86/kernel/smpboot.c 2011-03-11 09:29:46.000000000 -0600
@@ -1404,9 +1404,9 @@ 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;


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