Commit 6cb9a835 authored by Zachary Amsden's avatar Zachary Amsden Committed by Linus Torvalds

[PATCH] vmi: sched clock paravirt op fix

The custom_sched_clock hook is broken.  The result from sched_clock needs to
be in nanoseconds, not in CPU cycles.  The TSC is insufficient for this
purpose, because TSC is poorly defined in a virtual environment, and mostly
represents real world time instead of scheduled process time (which can be
interrupted without notice when a virtual machine is descheduled).

To make the scheduler consistent, we must expose a different nature of time,
that is scheduled time.  So deprecate this custom_sched_clock hack and turn it
into a paravirt-op, as it should have been all along.  This allows the tsc.c
code which converts cycles to nanoseconds to be shared by all paravirt-ops
backends.

It is unfortunate to add a new paravirt-op, but this is a very distinct
abstraction which is clearly different for all virtual machine
implementations, and it gets rid of an ugly indirect function which I
ashamedly admit I hacked in to try to get this to work earlier, and then even
got in the wrong units.
Signed-off-by: default avatarZachary Amsden <zach@vmware.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7507ba34
......@@ -32,6 +32,7 @@
#include <asm/fixmap.h>
#include <asm/apic.h>
#include <asm/tlbflush.h>
#include <asm/timer.h>
/* nop stub */
static void native_nop(void)
......@@ -520,6 +521,7 @@ struct paravirt_ops paravirt_ops = {
.write_msr = native_write_msr,
.read_tsc = native_read_tsc,
.read_pmc = native_read_pmc,
.get_scheduled_cycles = native_read_tsc,
.load_tr_desc = native_load_tr_desc,
.set_ldt = native_set_ldt,
.load_gdt = native_load_gdt,
......
......@@ -14,6 +14,7 @@
#include <asm/delay.h>
#include <asm/tsc.h>
#include <asm/io.h>
#include <asm/timer.h>
#include "mach_timer.h"
......@@ -102,9 +103,6 @@ unsigned long long sched_clock(void)
{
unsigned long long this_offset;
if (unlikely(custom_sched_clock))
return (*custom_sched_clock)();
/*
* Fall back to jiffies if there's no TSC available:
*/
......@@ -113,7 +111,7 @@ unsigned long long sched_clock(void)
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
/* read the Time Stamp Counter: */
rdtscll(this_offset);
get_scheduled_cycles(this_offset);
/* return the value in ns */
return cycles_2_ns(this_offset);
......
......@@ -873,7 +873,7 @@ static inline int __init activate_vmi(void)
paravirt_ops.setup_boot_clock = vmi_timer_setup_boot_alarm;
paravirt_ops.setup_secondary_clock = vmi_timer_setup_secondary_alarm;
#endif
custom_sched_clock = vmi_sched_clock;
paravirt_ops.get_scheduled_cycles = vmi_get_sched_cycles;
}
if (!disable_noidle)
para_fill(safe_halt, Halt);
......
......@@ -172,7 +172,7 @@ int vmi_set_wallclock(unsigned long now)
return -1;
}
unsigned long long vmi_sched_clock(void)
unsigned long long vmi_get_sched_cycles(void)
{
return read_available_cycles();
}
......
......@@ -94,6 +94,7 @@ struct paravirt_ops
u64 (*read_tsc)(void);
u64 (*read_pmc)(void);
u64 (*get_scheduled_cycles)(void);
void (*load_tr_desc)(void);
void (*load_gdt)(const struct Xgt_desc_struct *);
......@@ -273,6 +274,8 @@ static inline void halt(void)
#define rdtscll(val) (val = paravirt_ops.read_tsc())
#define get_scheduled_cycles(val) (val = paravirt_ops.get_scheduled_cycles())
#define write_tsc(val1,val2) wrmsr(0x10, val1, val2)
#define rdpmc(counter,low,high) do { \
......
......@@ -30,7 +30,6 @@ static inline int native_set_wallclock(unsigned long nowtime)
#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
extern unsigned long long native_sched_clock(void);
#else /* !CONFIG_PARAVIRT */
#define get_wallclock() native_get_wallclock()
......
......@@ -4,13 +4,19 @@
#include <linux/pm.h>
#define TICK_SIZE (tick_nsec / 1000)
void setup_pit_timer(void);
unsigned long long native_sched_clock(void);
/* Modifiers for buggy PIT handling */
extern int pit_latch_buggy;
extern int timer_ack;
extern int no_timer_check;
extern unsigned long long (*custom_sched_clock)(void);
extern int no_sync_cmos_clock;
extern int recalibrate_cpu_khz(void);
#ifndef CONFIG_PARAVIRT
#define get_scheduled_cycles(val) rdtscll(val)
#endif
#endif
......@@ -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_sched_clock(void);
extern unsigned long long vmi_get_sched_cycles(void);
#ifdef CONFIG_X86_LOCAL_APIC
extern void __init vmi_timer_setup_boot_alarm(void);
......
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