Messages in this thread Patch in this message | | | From | Yuyang Du <> | Subject | [PATCH v3 1/6] sched/fair: Generalize the load/util averages resolution definition | Date | Tue, 5 Apr 2016 12:12:26 +0800 |
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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> --- include/linux/sched.h | 16 +++++++++++++--- kernel/sched/fair.c | 4 ---- kernel/sched/sched.h | 15 ++++++++++----- 3 files changed, 23 insertions(+), 12 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h index 45e848c..bc652fe 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -935,9 +935,19 @@ enum cpu_idle_type { }; /* + * 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) /* @@ -1203,8 +1213,8 @@ 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: diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index b8cc1c3..88ab334 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -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) /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index a7cbad7..03ce2de 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -54,18 +54,23 @@ static inline void update_cpu_load_active(struct rq *this_rq) { } * increased costs. */ #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) +# 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 user) and its load (invisible to user) have + * independent ranges, but they should be well calibrated. We use scale_load() + * and scale_load_down(w) to convert between them, 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 -- 2.1.4
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