Re: [PATCH v4] sched/core: Preempt current task in favour of bound kthread

Peter Zijlstra
2019-12-12T10:14:41Z

On Thu, Dec 12, 2019 at 11:10:31AM +0100, Peter Zijlstra wrote:
> @@ -4156,13 +4159,13 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> if (delta_exec < sysctl_sched_min_granularity)
> return;
>
> - se = __pick_first_entity(cfs_rq);
> + se = __pick_next_entity(cfs_rq, NULL);
> delta = curr->vruntime - se->vruntime;
>
> if (delta < 0)
> return;

What I mean with the below comment is, when this isn't enough, try
something like:

if (se == cfs_rq->next)
ideal_runtime /= 2;

to make it yield sooner to 'next' buddies. Sadly, due to the whole
cgroup mess, we can't say what actual task is on the end of it (without
doing a full hierarchy pick, which is more expensive still).

> - if (delta > ideal_runtime)
> + if (delta > ideal_runtime) // maybe frob this too ?
> resched_curr(rq_of(cfs_rq));
> }