[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, 2 insertions, 4 deletions

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);