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.
Please apply.
Signed-off-by: Zachary Amsden <zach@vmware.com>
diff -r d58e6ddfdfa9 arch/i386/kernel/paravirt.c
--- a/arch/i386/kernel/paravirt.c Thu Feb 15 23:52:41 2007 -0800
+++ b/arch/i386/kernel/paravirt.c Fri Feb 16 00:04:39 2007 -0800
@@ -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,
diff -r d58e6ddfdfa9 arch/i386/kernel/tsc.c
--- a/arch/i386/kernel/tsc.c Thu Feb 15 23:52:41 2007 -0800
+++ b/arch/i386/kernel/tsc.c Fri Feb 16 00:06:34 2007 -0800
@@ -14,6 +14,7 @@
#include <asm/delay.h>
#include <asm/tsc.h>
#include <asm/io.h>
+#include <asm/timer.h>
#include "mach_timer.h"
@@ -108,9 +109,6 @@ 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:
*/
@@ -119,7 +117,7 @@ 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);
diff -r d58e6ddfdfa9 arch/i386/kernel/vmi.c
--- a/arch/i386/kernel/vmi.c Thu Feb 15 23:52:41 2007 -0800
+++ b/arch/i386/kernel/vmi.c Fri Feb 16 00:02:48 2007 -0800
@@ -873,7 +873,7 @@ static inline int __init activate_vmi(vo
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);
diff -r d58e6ddfdfa9 arch/i386/kernel/vmitime.c
--- a/arch/i386/kernel/vmitime.c Thu Feb 15 23:52:41 2007 -0800
+++ b/arch/i386/kernel/vmitime.c Fri Feb 16 00:02:48 2007 -0800
@@ -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();
}
diff -r d58e6ddfdfa9 include/asm-i386/paravirt.h
--- a/include/asm-i386/paravirt.h Thu Feb 15 23:52:41 2007 -0800
+++ b/include/asm-i386/paravirt.h Fri Feb 16 00:07:22 2007 -0800
@@ -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 { \
diff -r d58e6ddfdfa9 include/asm-i386/time.h
--- a/include/asm-i386/time.h Thu Feb 15 23:52:41 2007 -0800
+++ b/include/asm-i386/time.h Fri Feb 16 00:02:48 2007 -0800
@@ -30,7 +30,6 @@ static inline int native_set_wallclock(u
#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
-extern unsigned long long native_sched_clock(void);
#else /* !CONFIG_PARAVIRT */
#define get_wallclock() native_get_wallclock()
diff -r d58e6ddfdfa9 include/asm-i386/timer.h
--- a/include/asm-i386/timer.h Thu Feb 15 23:52:41 2007 -0800
+++ b/include/asm-i386/timer.h Fri Feb 16 00:05:13 2007 -0800
@@ -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
diff -r d58e6ddfdfa9 include/asm-i386/vmi_time.h
--- a/include/asm-i386/vmi_time.h Thu Feb 15 23:52:41 2007 -0800
+++ b/include/asm-i386/vmi_time.h Fri Feb 16 00:02:48 2007 -0800
@@ -49,7 +49,7 @@ extern void __init vmi_time_init(void);
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);