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

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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>
This commit is contained in:
Yuyang Du 2016-04-05 12:12:26 +08:00 committed by Ingo Molnar
parent 2159197d66
commit 6ecdd74962
3 changed files with 23 additions and 12 deletions
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16
include/linux/sched.h
View file

@ -936,10 +936,20 @@ enum cpu_idle_type {
CPU_MAX_IDLE_TYPES
};
/*
* Integer metrics need fixed point arithmetic, e.g., sched/fair
* has a few: load, load_avg, util_avg, freq, and capacity.
*
* We define a basic fixed point arithmetic range, and then formalize
* all these metrics based on that basic range.
*/
# define SCHED_FIXEDPOINT_SHIFT 10
# define SCHED_FIXEDPOINT_SCALE (1L << SCHED_FIXEDPOINT_SHIFT)
/*
* Increase resolution of cpu_capacity calculations
*/
#define SCHED_CAPACITY_SHIFT 10
#define SCHED_CAPACITY_SHIFT SCHED_FIXEDPOINT_SHIFT
#define SCHED_CAPACITY_SCALE (1L << SCHED_CAPACITY_SHIFT)
/*
@ -1205,8 +1215,8 @@ struct load_weight {
* 1) load_avg factors frequency scaling into the amount of time that a
* sched_entity is runnable on a rq into its weight. For cfs_rq, it is the
* aggregated such weights of all runnable and blocked sched_entities.
* 2) util_avg factors frequency and cpu scaling into the amount of time
* that a sched_entity is running on a CPU, in the range [0..SCHED_LOAD_SCALE].
* 2) util_avg factors frequency and cpu capacity scaling into the amount of time
* that a sched_entity is running on a CPU, in the range [0..SCHED_CAPACITY_SCALE].
* For cfs_rq, it is the aggregated such times of all runnable and
* blocked sched_entities.
* The 64 bit load_sum can:

4
kernel/sched/fair.c
View file

@ -2662,10 +2662,6 @@ static u32 __compute_runnable_contrib(u64 n)
return contrib + runnable_avg_yN_sum[n];
}
#if (SCHED_LOAD_SHIFT - SCHED_LOAD_RESOLUTION) != 10 || SCHED_CAPACITY_SHIFT != 10
#error "load tracking assumes 2^10 as unit"
#endif
#define cap_scale(v, s) ((v)*(s) >> SCHED_CAPACITY_SHIFT)
/*

15
kernel/sched/sched.h
View file

@ -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