On Thu, 16 Jul 2020 at 18:48, Dietmar Eggemann <dietmar.eggem...@arm.com> wrote: > > On 13/07/2020 14:59, Vincent Guittot wrote: > > On Fri, 10 Jul 2020 at 21:59, Patrick Bellasi > > <patrick.bell...@matbug.net> wrote: > >> > >> > >> On Fri, Jul 10, 2020 at 15:21:48 +0200, Vincent Guittot > >> <vincent.guit...@linaro.org> wrote... > > [...] > > >>> Instead, it should weight the decision in wakeup_preempt_entity() and > >>> wakeup_gran() > >> > >> In those functions we already take the task prio into consideration > >> (ref details at the end of this message). > >> > >> Lower nice value tasks have more chances to preempt current since they > >> will have a smaller wakeup_gran, indeed: > > > > yes, and this is there to ensure a fair distribution of running time > > and prevent a task to increase significantly its vruntime compare to > > others > > > > -1 min that se already got more runtime than current > > 0 that se's vruntime will go above current's vruntime after a runtime > > duration of sched_min_granularity > > and 1 means that se got less runtime than current and its vruntime > > will still be lower than current ones even after a runtime duration of > > sched_min_granularity > > > > IMHO, latency_nice should impact the decision only for case 0 but not > > the case -1 and 1. > > That being said, we can extend the case 0 a bit to include the > > situation where current's vruntime will become greater than se's > > vruntimes after a runtime duration of sched_min_granularity like > > below: > > > > curr->vruntime > > |<-- wakeup_gran(se) -->|<-- > > wakeupgran(curr) -->| > > current range: se->vruntime +1 | 0 | -1 > > new range: se->vruntime +1 | 0 > > | -1 > > > > I assume this got messed up by line break somehow:
yes > > curr->vruntime > |<-- wakeup_gran(se) -->|<-- > wakeup_gran(curr) -->| > current range: se->vruntime +1 | 0 | -1 > new range: se->vruntime +1 | 0 > | -1 > > IMHO, with the current use of wakeup_preempt_entity() I don't see what > will change with that. > We check 'wakeup_preempt_entity() == 1' in check_preempt_wakeup() and > 'wakeup_preempt_entity() < 1' in pick_next_entity(). > > How should the mapping between se's latency_nice value to the consideration of > wakeup_gran(curr) look like? IMO, the latency_nice can be used to move the +1|0 boundary on the right and the 0|-1 on the left with a formula that need to be defined And we also need to review where and how wakeup_preempt_entity is used > > [...]
