Re: [PATCH] sched/fair: set the se->vlag strictly following the paper

[Shijie Huang]

On 2025/6/19 21:53, Vincent Guittot wrote:
> On Thu, 19 Jun 2025 at 05:20, Huang Shijie
> <shijie@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> >  From the paper, the lag should follow the limit:
> >       -r_max < lag < max(r_max, q)
> >
> > But current code makes the lag follow the limit:
> >       -max(r_max, q) < lag < max(r_max, q)
> >
> > This patch introduces limit_hi/limit_lo/r_max, and
> > make the lag follow the paper strictly.
> We don't strictly follow the paper. Typically, paper assumes that a
> task will not run more than its slice r before deciding which task is
> the next to run. But this is not our case as we must wait for a sched
> event like the tick before picking next  task which can be longer than
> the slice r
>
> Side note, we don't have a fix definition of the quantum q which is
> something between 0 and a tick (and even more currently with run to
> parity) as we wait for the next the tick to pick another task
>
> This means that a task can run a full tick period even if its slice is
> shorter than the tick period

Thanks for the explanations.

But if we enable the HRTICK, the task will run to match its slice.


Thanks

Huang Shijie