On Tue, Nov 17, 2020 at 06:19:38PM -0500, Joel Fernandes (Google) wrote:
> From: Vineeth Pillai <virem...@linux.microsoft.com>
>
> If there is only one long running local task and the sibling is
> forced idle, it might not get a chance to run until a schedule
> event happens on any cpu in the core.
>
> So we check for this condition during a tick to see if a sibling
> is starved and then give it a chance to schedule.
>
> Tested-by: Julien Desfossez <jdesfos...@digitalocean.com>
> Reviewed-by: Joel Fernandes (Google) <j...@joelfernandes.org>
> Signed-off-by: Vineeth Pillai <virem...@linux.microsoft.com>
> Signed-off-by: Julien Desfossez <jdesfos...@digitalocean.com>
> Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
> ---
> kernel/sched/core.c | 15 ++++++++-------
> kernel/sched/fair.c | 40 ++++++++++++++++++++++++++++++++++++++++
> kernel/sched/sched.h | 2 +-
> 3 files changed, 49 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1bd0b0bbb040..52d0e83072a4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5206,16 +5206,15 @@ pick_next_task(struct rq *rq, struct task_struct
> *prev, struct rq_flags *rf)
>
> /* reset state */
> rq->core->core_cookie = 0UL;
> + if (rq->core->core_forceidle) {
> + need_sync = true;
> + rq->core->core_forceidle = false;
> + }
> for_each_cpu(i, smt_mask) {
> struct rq *rq_i = cpu_rq(i);
>
> rq_i->core_pick = NULL;
>
> - if (rq_i->core_forceidle) {
> - need_sync = true;
> - rq_i->core_forceidle = false;
> - }
> -
> if (i != cpu)
> update_rq_clock(rq_i);
> }
> @@ -5335,8 +5334,10 @@ next_class:;
> if (!rq_i->core_pick)
> continue;
>
> - if (is_task_rq_idle(rq_i->core_pick) && rq_i->nr_running)
> - rq_i->core_forceidle = true;
> + if (is_task_rq_idle(rq_i->core_pick) && rq_i->nr_running &&
> + !rq_i->core->core_forceidle) {
> + rq_i->core->core_forceidle = true;
> + }
>
> if (i == cpu) {
> rq_i->core_pick = NULL;
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f53681cd263e..42965c4fd71f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10692,6 +10692,44 @@ static void rq_offline_fair(struct rq *rq)
>
> #endif /* CONFIG_SMP */
>
> +#ifdef CONFIG_SCHED_CORE
> +static inline bool
> +__entity_slice_used(struct sched_entity *se, int min_nr_tasks)
> +{
> + u64 slice = sched_slice(cfs_rq_of(se), se);
I wonder if the definition of sched_slice() should be revisited for core
scheduling?
Should we use sched_slice = sched_slice / cpumask_weight(smt_mask)?
Would that resolve the issue your seeing? Effectively we need to answer
if two sched core siblings should be treated as executing one large
slice?
Balbir Singh.
