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authorGuillaume Chazarain <guichaz@yahoo.fr>2008-01-30 13:30:06 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-30 13:30:06 +0100
commit53d517cdbaac704352b3d0c10fecb99e0b54572e (patch)
tree4056bc99a4e6077d7d968d30ea21895e425a83ef /include/asm-x86/timer.h
parent83bd01024b1fdfc41d9b758e5669e80fca72df66 (diff)
x86: scale cyc_2_nsec according to CPU frequency
scale the sched_clock() cyc_2_nsec scaling factor according to CPU frequency changes. [ mingo@elte.hu: simplified it and fixed it for SMP. ] Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'include/asm-x86/timer.h')
-rw-r--r--include/asm-x86/timer.h23
1 files changed, 18 insertions, 5 deletions
diff --git a/include/asm-x86/timer.h b/include/asm-x86/timer.h
index 0db7e994fb8..4f6fcb050c1 100644
--- a/include/asm-x86/timer.h
+++ b/include/asm-x86/timer.h
@@ -2,6 +2,7 @@
#define _ASMi386_TIMER_H
#include <linux/init.h>
#include <linux/pm.h>
+#include <linux/percpu.h>
#define TICK_SIZE (tick_nsec / 1000)
@@ -16,7 +17,7 @@ extern int recalibrate_cpu_khz(void);
#define calculate_cpu_khz() native_calculate_cpu_khz()
#endif
-/* Accellerators for sched_clock()
+/* Accelerators for sched_clock()
* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
* ns = cycles / (freq / ns_per_sec)
@@ -31,20 +32,32 @@ extern int recalibrate_cpu_khz(void);
* And since SC is a constant power of two, we can convert the div
* into a shift.
*
- * We can use khz divisor instead of mhz to keep a better percision, since
+ * We can use khz divisor instead of mhz to keep a better precision, since
* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* (mathieu.desnoyers@polymtl.ca)
*
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*/
-extern unsigned long cyc2ns_scale __read_mostly;
+
+DECLARE_PER_CPU(unsigned long, cyc2ns);
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
-static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
{
- return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
+ return cyc * per_cpu(cyc2ns, smp_processor_id()) >> CYC2NS_SCALE_FACTOR;
}
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+ unsigned long long ns;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ ns = __cycles_2_ns(cyc);
+ local_irq_restore(flags);
+
+ return ns;
+}
#endif