[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: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 6 insertions, 6 deletions

diff --git a/arch/i386/kernel/paravirt.c b/arch/i386/kernel/paravirt.c
index c156ecfa3872..31bbe70d1e02 100644
--- a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -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 --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index 3082a418635c..c9c9d54c91f6 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -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);
diff --git a/arch/i386/kernel/vmi.c b/arch/i386/kernel/vmi.c
index 8417f741fac8..556b9a6b7365 100644
--- a/arch/i386/kernel/vmi.c
+++ b/arch/i386/kernel/vmi.c
@@ -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);
diff --git a/arch/i386/kernel/vmitime.c b/arch/i386/kernel/vmitime.c
index 694aa85d22c2..f2aa8fab8c02 100644
--- a/arch/i386/kernel/vmitime.c
+++ b/arch/i386/kernel/vmitime.c
@@ -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();
 }