On 3 March 2015 at 13:47, Dietmar Eggemann <dietmar.eggem...@arm.com> wrote: > On 27/02/15 15:54, Vincent Guittot wrote: >> Monitor the usage level of each group of each sched_domain level. The usage >> is >> the portion of cpu_capacity_orig that is currently used on a CPU or group of >> CPUs. We use the utilization_load_avg to evaluate the usage level of each >> group. >> >> The utilization_load_avg only takes into account the running time of the CFS >> tasks on a CPU with a maximum value of SCHED_LOAD_SCALE when the CPU is fully >> utilized. Nevertheless, we must cap utilization_load_avg which can be >> temporaly > > s/temporaly/temporally > >> greater than SCHED_LOAD_SCALE after the migration of a task on this CPU and >> until the metrics are stabilized. >> >> The utilization_load_avg is in the range [0..SCHED_LOAD_SCALE] to reflect the >> running load on the CPU whereas the available capacity for the CFS task is in >> the range [0..cpu_capacity_orig]. In order to test if a CPU is fully utilized >> by CFS tasks, we have to scale the utilization in the cpu_capacity_orig range >> of the CPU to get the usage of the latter. The usage can then be compared >> with >> the available capacity (ie cpu_capacity) to deduct the usage level of a CPU. >> >> The frequency scaling invariance of the usage is not taken into account in >> this >> patch, it will be solved in another patch which will deal with frequency >> scaling invariance on the running_load_avg. > > 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. > >> >> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> >> Acked-by: Morten Rasmussen <morten.rasmus...@arm.com> >> --- >> kernel/sched/fair.c | 29 +++++++++++++++++++++++++++++ >> 1 file changed, 29 insertions(+) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 10f84c3..faf61a2 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -4781,6 +4781,33 @@ static int select_idle_sibling(struct task_struct *p, >> int target) >> done: >> return target; >> } >> +/* >> + * get_cpu_usage returns the amount of capacity of a CPU that is used by CFS >> + * tasks. The unit of the return value must capacity so we can compare the > > s/must capacity/must be the one of capacity > >> + * usage with the capacity of the CPU that is available for CFS task (ie >> + * cpu_capacity). >> + * cfs.utilization_load_avg is the sum of running time of runnable tasks on >> a >> + * CPU. It represents the amount of utilization of a CPU in the range >> + * [0..SCHED_LOAD_SCALE]. The usage of a CPU can't be higher than the full >> + * capacity of the CPU because it's about the running time on this CPU. >> + * Nevertheless, cfs.utilization_load_avg can be higher than >> SCHED_LOAD_SCALE >> + * because of unfortunate rounding in avg_period and running_load_avg or >> just >> + * after migrating tasks until the average stabilizes with the new running >> + * time. So we need to check that the usage stays into the range >> + * [0..cpu_capacity_orig] and cap if necessary. >> + * Without capping the usage, a group could be seen as overloaded (CPU0 >> usage >> + * at 121% + CPU1 usage at 80%) whereas CPU1 has 20% of available capacity/ > > s/capacity\//capacity.
I have resent the patch with typo correction > > [...] > > -- Dietmar > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
