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Commit 688340ea authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Jeremy Fitzhardinge
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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: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Dan Hecht <dhecht@vmware.com>
Cc: john stultz <johnstul@us.ibm.com>
parent d572929c

arch/i386/kernel/paravirt.c

+1 −1
Original line number Diff line number Diff line
@@ -302,7 +302,7 @@ struct paravirt_ops paravirt_ops = { 
	.write_msr = native_write_msr_safe,

	.read_tsc = native_read_tsc,

	.read_pmc = native_read_pmc,

	.get_scheduled_cycles = native_read_tsc,

	.sched_clock = native_sched_clock,

	.get_cpu_khz = native_calculate_cpu_khz,

	.load_tr_desc = native_load_tr_desc,

	.set_ldt = native_set_ldt,

arch/i386/kernel/tsc.c

+15 −8
Original line number Diff line number Diff line
@@ -84,7 +84,7 @@ static inline int check_tsc_unstable(void) 
 *

 *			-johnstul@us.ibm.com "math is hard, lets go shopping!"

 */

static unsigned long cyc2ns_scale __read_mostly;

unsigned long cyc2ns_scale __read_mostly;



#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
@@ -93,15 +93,10 @@ static inline void set_cyc2ns_scale(unsigned long cpu_khz) 
	cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;

}



static inline unsigned long long cycles_2_ns(unsigned long long cyc)

{

	return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;

}



/*

 * Scheduler clock - returns current time in nanosec units.

 */

unsigned long long sched_clock(void)

unsigned long long native_sched_clock(void)

{

	unsigned long long this_offset;
@@ -118,12 +113,24 @@ unsigned long long sched_clock(void) 
		return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);



	/* read the Time Stamp Counter: */

	get_scheduled_cycles(this_offset);

	rdtscll(this_offset);



	/* return the value in ns */

	return cycles_2_ns(this_offset);

}



/* We need to define a real function for sched_clock, to override the

   weak default version */

#ifdef CONFIG_PARAVIRT

unsigned long long sched_clock(void)

{

	return paravirt_sched_clock();

}

#else

unsigned long long sched_clock(void)

	__attribute__((alias("native_sched_clock")));

#endif



unsigned long native_calculate_cpu_khz(void)

{

	unsigned long long start, end;

arch/i386/kernel/vmi.c

+1 −1
Original line number Diff line number Diff line
@@ -891,7 +891,7 @@ static inline int __init activate_vmi(void) 
		paravirt_ops.setup_boot_clock = vmi_time_bsp_init;

		paravirt_ops.setup_secondary_clock = vmi_time_ap_init;

#endif

		paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles;

		paravirt_ops.sched_clock = vmi_sched_clock;

 		paravirt_ops.get_cpu_khz = vmi_cpu_khz;



		/* We have true wallclock functions; disable CMOS clock sync */

arch/i386/kernel/vmiclock.c

+3 −3
Original line number Diff line number Diff line
@@ -64,10 +64,10 @@ int vmi_set_wallclock(unsigned long now) 
	return 0;

}



/* paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles */

unsigned long long vmi_get_sched_cycles(void)

/* paravirt_ops.sched_clock = vmi_sched_clock */

unsigned long long vmi_sched_clock(void)

{

	return vmi_timer_ops.get_cycle_counter(VMI_CYCLES_AVAILABLE);

	return cycles_2_ns(vmi_timer_ops.get_cycle_counter(VMI_CYCLES_AVAILABLE));

}



/* paravirt_ops.get_cpu_khz = vmi_cpu_khz */

include/asm-i386/paravirt.h

+5 −2
Original line number Diff line number Diff line
@@ -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)