sched/fair: Generalize the load/util averages resolution definition

Integer metric needs fixed point arithmetic. In sched/fair, a few
metrics, e.g., weight, load, load_avg, util_avg, freq, and capacity,
may have different fixed point ranges, which makes their update and
usage error-prone.

In order to avoid the errors relating to the fixed point range, we
definie a basic fixed point range, and then formalize all metrics to
base on the basic range.

The basic range is 1024 or (1 << 10). Further, one can recursively
apply the basic range to have larger range.

Pointed out by Ben Segall, weight (visible to user, e.g., NICE-0 has
1024) and load (e.g., NICE_0_LOAD) have independent ranges, but they
must be well calibrated.

Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Cc: dietmar.eggemann@arm.com
Cc: lizefan@huawei.com
Cc: morten.rasmussen@arm.com
Cc: pjt@google.com
Cc: umgwanakikbuti@gmail.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1459829551-21625-2-git-send-email-yuyang.du@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 10 insertions, 5 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 066a4c2d2695..ad83361f9e67 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -56,18 +56,23 @@ static inline void cpu_load_update_active(struct rq *this_rq) { }
  * increase coverage and consistency always enable it on 64bit platforms.
  */
 #ifdef CONFIG_64BIT
-# define SCHED_LOAD_RESOLUTION  10
-# define scale_load(w)          ((w) << SCHED_LOAD_RESOLUTION)
-# define scale_load_down(w)     ((w) >> SCHED_LOAD_RESOLUTION)
+# define SCHED_LOAD_SHIFT       (SCHED_FIXEDPOINT_SHIFT + SCHED_FIXEDPOINT_SHIFT)
+# define scale_load(w)          ((w) << SCHED_FIXEDPOINT_SHIFT)
+# define scale_load_down(w)     ((w) >> SCHED_FIXEDPOINT_SHIFT)
 #else
-# define SCHED_LOAD_RESOLUTION  0
+# define SCHED_LOAD_SHIFT       (SCHED_FIXEDPOINT_SHIFT)
 # define scale_load(w)          (w)
 # define scale_load_down(w)     (w)
 #endif
 
-#define SCHED_LOAD_SHIFT        (10 + SCHED_LOAD_RESOLUTION)
 #define SCHED_LOAD_SCALE        (1L << SCHED_LOAD_SHIFT)
 
+/*
+ * NICE_0's weight (visible to users) and its load (invisible to users) have
+ * independent ranges, but they should be well calibrated. We use scale_load()
+ * and scale_load_down(w) to convert between them, and the following must be true:
+ * scale_load(sched_prio_to_weight[20]) == NICE_0_LOAD
+ */
 #define NICE_0_LOAD             SCHED_LOAD_SCALE
 #define NICE_0_SHIFT            SCHED_LOAD_SHIFT