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Add a sched_clock paravirt_op

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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 <[email protected]>
Cc: Zachary Amsden <[email protected]>
Cc: Dan Hecht <[email protected]>
Cc: john stultz <[email protected]>
This commit is contained in:
Jeremy Fitzhardinge 2007-07-17 18:37:04 -07:00 • committed by Jeremy Fitzhardinge
commit 688340ea34
7 changed files with 57 additions and 17 deletions
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7
include/asm-i386/paravirt.h
View file

@ -118,7 +118,7 @@ struct paravirt_ops
u64 (*read_tsc)(void);
u64 (*read_pmc)(void);
u64 (*get_scheduled_cycles)(void);
unsigned long long (*sched_clock)(void);
unsigned long (*get_cpu_khz)(void);
/* Segment descriptor handling */
@ -566,7 +566,10 @@ static inline u64 paravirt_read_tsc(void)
#define rdtscll(val) (val = paravirt_read_tsc())
#define get_scheduled_cycles(val) (val = paravirt_ops.get_scheduled_cycles())
static inline unsigned long long paravirt_sched_clock(void)
{
return PVOP_CALL0(unsigned long long, sched_clock);
}
#define calculate_cpu_khz() (paravirt_ops.get_cpu_khz())
#define write_tsc(val1,val2) wrmsr(0x10, val1, val2)

32
include/asm-i386/timer.h
View file

@ -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

2
include/asm-i386/vmi_time.h
View file

@ -49,7 +49,7 @@ extern struct vmi_timer_ops {
extern void __init vmi_time_init(void);
extern unsigned long vmi_get_wallclock(void);
extern int vmi_set_wallclock(unsigned long now);
extern unsigned long long vmi_get_sched_cycles(void);
extern unsigned long long vmi_sched_clock(void);
extern unsigned long vmi_cpu_khz(void);
#ifdef CONFIG_X86_LOCAL_APIC