Messages in this thread | | | Date | Wed, 17 Aug 2022 17:03:17 +0200 | Subject | Re: [PATCH] sched/topology: Remove EM_MAX_COMPLEXITY limit | From | Pierre Gondois <> |
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Hi Ionela,
On 8/17/22 16:21, Ionela Voinescu wrote: > Hi Pierre, > > On Friday 12 Aug 2022 at 12:16:19 (+0200), Pierre Gondois wrote: >> From: Pierre Gondois <Pierre.Gondois@arm.com> >> >> The Energy Aware Scheduler (EAS) estimates the energy consumption >> of placing a task on different CPUs. The goal is to minimize this >> energy consumption. Estimating the energy of different task placements >> is increasingly complex with the size of the platform. To avoid having >> a slow wake-up path, EAS is only enabled if this complexity is low >> enough. >> >> The current complexity limit was set in: >> commit b68a4c0dba3b1 ("sched/topology: Disable EAS on inappropriate >> platforms"). >> base on the first implementation of EAS, which was re-computing >> the power of the whole platform for each task placement scenario, cf: >> commit 390031e4c309 ("sched/fair: Introduce an energy estimation helper >> function"). >> but the complexity of EAS was reduced in: >> commit eb92692b2544d ("sched/fair: Speed-up energy-aware wake-ups") >> and find_energy_efficient_cpu() (feec) algorithm was updated in: >> commit 3e8c6c9aac42 ("sched/fair: Remove task_util from effective >> utilization in feec()") >> >> find_energy_efficient_cpu() (feec) is now doing: >> feec() >> \_ for_each_pd(pd) [0] >> // get max_spare_cap_cpu and compute_prev_delta >> \_ for_each_cpu(pd) [1] >> >> \_ get_pd_busy_time(pd) [2] >> \_ for_each_cpu(pd) >> >> // evaluate pd energy without the task >> \_ get_pd_max_util(pd, -1) [3.0] >> \_ for_each_cpu(pd) >> \_ compute_energy(pd, -1) >> \_ for_each_ps(pd) >> >> // evaluate pd energy with the task on prev_cpu >> \_ get_pd_max_util(pd, prev_cpu) [3.1] >> \_ for_each_cpu(pd) >> \_ compute_energy(pd, prev_cpu) >> \_ for_each_ps(pd) >> >> // evaluate pd energy with the task on max_spare_cap_cpu >> \_ get_pd_max_util(pd, max_spare_cap_cpu) [3.2] >> \_ for_each_cpu(pd) >> \_ compute_energy(pd, max_spare_cap_cpu) >> \_ for_each_ps(pd) >> >> [3.1] happens only once since prev_cpu is unique. To have an upper >> bound of the complexity, [3.1] is taken into account for all pds. >> So with the same definitions for nr_pd, nr_cpus and nr_ps, >> the complexity is of: >> nr_pd * (2 * [nr_cpus in pd] + 3 * ([nr_cpus in pd] + [nr_ps in pd])) >> [0] * ( [1] + [2] + [3.0] + [3.1] + [3.2] ) >> = 5 * nr_cpus + 3 * nr_ps >> > > I just want to draw your attention to [1] and the fact that the > structure of the function changed. Your calculations largely remain the > same - 3 calls to compute_energy() which in turn now calls > eenv_pd_max_util() with operations for each cpu, plus some scattered > calls to eenv_pd_busy_time(), all for each pd.
Yes indeed, there is: s/get_pd_max_util/eenv_pd_max_util
and also as you spotted, the following pattern: \_ eenv_pd_max_util(pd, dst_cpu) \_ for_each_cpu(pd) \_ compute_energy(pd, dst_cpu) \_ for_each_ps(pd)
should actually be: \_ compute_energy(pd, dst_cpu) \_ eenv_pd_max_util(pd, dst_cpu) \_ for_each_cpu(pd) \_ for_each_ps(pd)
Thanks, Pierre
> > [1] > https://lore.kernel.org/lkml/20220621090414.433602-7-vdonnefort@google.com/ > > Thanks, > Ionela.
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