[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>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/asm-i386/vmi_time.h b/include/asm-i386/vmi_time.h
index c12931211007..f59c35d37352 100644
--- a/include/asm-i386/vmi_time.h
+++ b/include/asm-i386/vmi_time.h
@@ -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);