[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, 7 insertions, 1 deletions

diff --git a/include/asm-i386/timer.h b/include/asm-i386/timer.h
index 4752c3a..d1f7b4f 100644
--- a/include/asm-i386/timer.h
+++ b/include/asm-i386/timer.h
@@ -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