On 27/02/15 15:54, Vincent Guittot wrote:
From: Morten Rasmussen morten.rasmussen@arm.com
Apply frequency scale-invariance correction factor to usage tracking. Each segment of the running_load_avg geometric series is now scaled by the
The same comment I sent out on [PATCH v10 07/11]:
The use of underscores in running_load_avg implies to me that this is a data member of struct sched_avg or something similar. But there is no running_load_avg in the current code. However, I can see that sched_avg::*running_avg_sum* (and therefore cfs_rq::*utilization_load_avg*) are frequency scale invariant.
-- Dietmar
current frequency so the utilization_avg_contrib of each entity will be invariant with frequency scaling. As a result, utilization_load_avg which is the sum of utilization_avg_contrib, becomes invariant too. So the usage level that is returned by get_cpu_usage, stays relative to the max frequency as the cpu_capacity which is is compared against. Then, we want the keep the load tracking values in a 32bits type, which implies that the max value of {runnable|running}_avg_sum must be lower than 2^32/88761=48388 (88761 is the max weigth of a task). As LOAD_AVG_MAX = 47742, arch_scale_freq_capacity must return a value less than (48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY = 1024). So we define the range to [0..SCHED_SCALE_CAPACITY] in order to avoid overflow.