sched: Disable (revert) SCHED_LOAD_SCALE increase

Alex reported that commit c8b281161df ("sched: Increase
SCHED_LOAD_SCALE resolution") caused a power usage regression
under light load as it increases the number of load-balance
operations and keeps idle cpus from staying idle.

Time has run out to find the root cause for this release so
disable the feature for v3.0 until we can figure out what
causes the problem.

Reported-by: "Alex, Shi" <alex.shi@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nikhil Rao <ncrao@google.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-m4onxn0sxnyn5iz9o88eskc3@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a837b20ba190330c23b59ec5a3fb584fc9f6308f..496770a96487676ec12f222d97a4af8defcf341b 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -808,7 +808,7 @@ enum cpu_idle_type {
  * when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
  * increased costs.
  */
-#if BITS_PER_LONG > 32
+#if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load  */
 # define SCHED_LOAD_RESOLUTION 10
 # define scale_load(w)         ((w) << SCHED_LOAD_RESOLUTION)
 # define scale_load_down(w)    ((w) >> SCHED_LOAD_RESOLUTION)