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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 <jeremy@xensource.com> Cc: Zachary Amsden <zach@vmware.com> Cc: Dan Hecht <dhecht@vmware.com> Cc: john stultz <johnstul@us.ibm.com>
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7 changed files with 57 additions and 17 deletions
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@ -302,7 +302,7 @@ struct paravirt_ops paravirt_ops = {
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.write_msr = native_write_msr_safe,
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.read_tsc = native_read_tsc,
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.read_pmc = native_read_pmc,
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.get_scheduled_cycles = native_read_tsc,
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.sched_clock = native_sched_clock,
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.get_cpu_khz = native_calculate_cpu_khz,
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.load_tr_desc = native_load_tr_desc,
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.set_ldt = native_set_ldt,
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@ -84,7 +84,7 @@ static inline int check_tsc_unstable(void)
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*
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* -johnstul@us.ibm.com "math is hard, lets go shopping!"
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*/
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static unsigned long cyc2ns_scale __read_mostly;
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unsigned long cyc2ns_scale __read_mostly;
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#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
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@ -93,15 +93,10 @@ static inline void set_cyc2ns_scale(unsigned long cpu_khz)
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cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
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}
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static inline unsigned long long cycles_2_ns(unsigned long long cyc)
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{
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return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
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}
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/*
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* Scheduler clock - returns current time in nanosec units.
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*/
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unsigned long long sched_clock(void)
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unsigned long long native_sched_clock(void)
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{
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unsigned long long this_offset;
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@ -118,12 +113,24 @@ unsigned long long sched_clock(void)
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return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
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/* read the Time Stamp Counter: */
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get_scheduled_cycles(this_offset);
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rdtscll(this_offset);
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/* return the value in ns */
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return cycles_2_ns(this_offset);
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}
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/* We need to define a real function for sched_clock, to override the
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weak default version */
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#ifdef CONFIG_PARAVIRT
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unsigned long long sched_clock(void)
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{
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return paravirt_sched_clock();
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}
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#else
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unsigned long long sched_clock(void)
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__attribute__((alias("native_sched_clock")));
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#endif
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unsigned long native_calculate_cpu_khz(void)
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{
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unsigned long long start, end;
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@ -891,7 +891,7 @@ static inline int __init activate_vmi(void)
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paravirt_ops.setup_boot_clock = vmi_time_bsp_init;
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paravirt_ops.setup_secondary_clock = vmi_time_ap_init;
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#endif
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paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles;
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paravirt_ops.sched_clock = vmi_sched_clock;
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paravirt_ops.get_cpu_khz = vmi_cpu_khz;
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/* We have true wallclock functions; disable CMOS clock sync */
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@ -64,10 +64,10 @@ int vmi_set_wallclock(unsigned long now)
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return 0;
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}
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/* paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles */
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unsigned long long vmi_get_sched_cycles(void)
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/* paravirt_ops.sched_clock = vmi_sched_clock */
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unsigned long long vmi_sched_clock(void)
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{
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return vmi_timer_ops.get_cycle_counter(VMI_CYCLES_AVAILABLE);
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return cycles_2_ns(vmi_timer_ops.get_cycle_counter(VMI_CYCLES_AVAILABLE));
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}
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/* paravirt_ops.get_cpu_khz = vmi_cpu_khz */
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@ -118,7 +118,7 @@ struct paravirt_ops
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u64 (*read_tsc)(void);
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u64 (*read_pmc)(void);
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u64 (*get_scheduled_cycles)(void);
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unsigned long long (*sched_clock)(void);
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unsigned long (*get_cpu_khz)(void);
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/* Segment descriptor handling */
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@ -566,7 +566,10 @@ static inline u64 paravirt_read_tsc(void)
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#define rdtscll(val) (val = paravirt_read_tsc())
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#define get_scheduled_cycles(val) (val = paravirt_ops.get_scheduled_cycles())
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static inline unsigned long long paravirt_sched_clock(void)
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{
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return PVOP_CALL0(unsigned long long, sched_clock);
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}
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#define calculate_cpu_khz() (paravirt_ops.get_cpu_khz())
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#define write_tsc(val1,val2) wrmsr(0x10, val1, val2)
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@ -15,8 +15,38 @@ extern int no_sync_cmos_clock;
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extern int recalibrate_cpu_khz(void);
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#ifndef CONFIG_PARAVIRT
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#define get_scheduled_cycles(val) rdtscll(val)
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#define calculate_cpu_khz() native_calculate_cpu_khz()
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#endif
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/* Accellerators for sched_clock()
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* convert from cycles(64bits) => nanoseconds (64bits)
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* basic equation:
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* ns = cycles / (freq / ns_per_sec)
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* ns = cycles * (ns_per_sec / freq)
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* ns = cycles * (10^9 / (cpu_khz * 10^3))
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* ns = cycles * (10^6 / cpu_khz)
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*
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* Then we use scaling math (suggested by george@mvista.com) to get:
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* ns = cycles * (10^6 * SC / cpu_khz) / SC
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* ns = cycles * cyc2ns_scale / SC
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*
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* And since SC is a constant power of two, we can convert the div
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* into a shift.
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*
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* We can use khz divisor instead of mhz to keep a better percision, since
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* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
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* (mathieu.desnoyers@polymtl.ca)
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*
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* -johnstul@us.ibm.com "math is hard, lets go shopping!"
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*/
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extern unsigned long cyc2ns_scale __read_mostly;
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#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
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static inline unsigned long long cycles_2_ns(unsigned long long cyc)
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{
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return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
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}
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#endif
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@ -49,7 +49,7 @@ extern struct vmi_timer_ops {
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extern void __init vmi_time_init(void);
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extern unsigned long vmi_get_wallclock(void);
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extern int vmi_set_wallclock(unsigned long now);
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extern unsigned long long vmi_get_sched_cycles(void);
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extern unsigned long long vmi_sched_clock(void);
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extern unsigned long vmi_cpu_khz(void);
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#ifdef CONFIG_X86_LOCAL_APIC
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