Hi Hillf,
On Fri, 16 Sept 2022 at 14:03, Hillf Danton <hdanton@xxxxxxxx> wrote:
>
> Hello Vincent
>
> On 16 Sep 2022 10:03:02 +0200 Vincent Guittot <vincent.guittot@xxxxxxxxxx> wrote:
> >
> > @@ -4606,6 +4608,7 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> >
> > se = __pick_first_entity(cfs_rq);
> > delta = curr->vruntime - se->vruntime;
> > + delta -= wakeup_latency_gran(curr, se);
> >
> > if (delta < 0)
> > return;
>
> What is derived from the latency nice you added is the runtime granulaity
> which has a role in preempting the current task.
>
> Given the same defination of latency nice as the nice, the runtime granularity
> can be computed without introducing the latency nice.
>
> Only for thoughts now.
>
> Hillf
>
> +++ b/kernel/sched/fair.c
> @@ -4569,7 +4569,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
> static void
> check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> {
> - unsigned long ideal_runtime, delta_exec;
> + unsigned long ideal_runtime, delta_exec, granu;
> struct sched_entity *se;
> s64 delta;
>
> @@ -4594,6 +4594,14 @@ check_preempt_tick(struct cfs_rq *cfs_rq
> return;
>
> se = __pick_first_entity(cfs_rq);
> +
> + granu = sysctl_sched_min_granularity +
> + (ideal_runtime - sysctl_sched_min_granularity) *
> + (se->latency_nice + 20) / LATENCY_NICE_WIDTH;
There is no latency_nice field in se but a latency_offset instead
Also at this step, we are sure that curr has run at least
sysctl_sched_min_granularity and we want now to compare curr vruntime
with first se's one. We take the latency offset into account to make
sure we will not preempt curr too early
> +
> + if (delta_exec < granu)
> + return;
> +
> delta = curr->vruntime - se->vruntime;
>
> if (delta < 0)
