From 688340ea34c61ad12473ccd837325b59aada9a93 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Tue, 17 Jul 2007 18:37:04 -0700 Subject: Add a sched_clock paravirt_op The tsc-based get_scheduled_cycles interface is not a good match for Xen's runstate accounting, which reports everything in nanoseconds. This patch replaces this interface with a sched_clock interface, which matches both Xen and VMI's requirements. In order to do this, we: 1. replace get_scheduled_cycles with sched_clock 2. hoist cycles_2_ns into a common header 3. update vmi accordingly One thing to note: because sched_clock is implemented as a weak function in kernel/sched.c, we must define a real function in order to override this weak binding. This means the usual paravirt_ops technique of using an inline function won't work in this case. Signed-off-by: Jeremy Fitzhardinge Cc: Zachary Amsden Cc: Dan Hecht Cc: john stultz --- include/asm-i386/timer.h | 32 +++++++++++++++++++++++++++++++- 1 file changed, 31 insertions(+), 1 deletion(-) (limited to 'include/asm-i386/timer.h') diff --git a/include/asm-i386/timer.h b/include/asm-i386/timer.h index 153770e25faa..51a713e33a9e 100644 --- a/include/asm-i386/timer.h +++ b/include/asm-i386/timer.h @@ -15,8 +15,38 @@ extern int no_sync_cmos_clock; extern int recalibrate_cpu_khz(void); #ifndef CONFIG_PARAVIRT -#define get_scheduled_cycles(val) rdtscll(val) #define calculate_cpu_khz() native_calculate_cpu_khz() #endif +/* Accellerators for sched_clock() + * convert from cycles(64bits) => nanoseconds (64bits) + * basic equation: + * ns = cycles / (freq / ns_per_sec) + * ns = cycles * (ns_per_sec / freq) + * ns = cycles * (10^9 / (cpu_khz * 10^3)) + * ns = cycles * (10^6 / cpu_khz) + * + * Then we use scaling math (suggested by george@mvista.com) to get: + * ns = cycles * (10^6 * SC / cpu_khz) / SC + * ns = cycles * cyc2ns_scale / SC + * + * 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 + * 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; + +#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */ + +static inline unsigned long long cycles_2_ns(unsigned long long cyc) +{ + return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR; +} + + #endif -- cgit v1.2.2