Commit-ID: 6ecdd74962f246dfe8750b7bea481a1c0816315d Gitweb: http://git.kernel.org/tip/6ecdd74962f246dfe8750b7bea481a1c0816315d Author: Yuyang Du <yuyang...@intel.com> AuthorDate: Tue, 5 Apr 2016 12:12:26 +0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 5 May 2016 09:24:00 +0200
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...@intel.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Mike Galbraith <efa...@gmx.de> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: bseg...@google.com Cc: dietmar.eggem...@arm.com Cc: lize...@huawei.com Cc: morten.rasmus...@arm.com Cc: p...@google.com Cc: umgwanakikb...@gmail.com Cc: vincent.guit...@linaro.org Link: http://lkml.kernel.org/r/1459829551-21625-2-git-send-email-yuyang...@intel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- 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 d894f2d..7d779d7 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -937,9 +937,19 @@ 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) /* @@ -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: diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 91395e1..76ca86e 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 066a4c2..ad83361 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
