[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, 3 insertions, 0 deletions

diff --git a/include/asm-i386/paravirt.h b/include/asm-i386/paravirt.h
index 6317e0a4d735..a13230254f4f 100644
--- a/include/asm-i386/paravirt.h
+++ b/include/asm-i386/paravirt.h
@@ -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 {                            \