Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 6 Jul 2022 12:47:44 +0200 | Subject | Re: [PATCH 3/3] sched/deadline: Use sched_dl_entity's dl_density in dl_task_fits_capacity() |
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On Wed, 29 Jun 2022 at 14:21, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > Save a multiplication in dl_task_fits_capacity() by using already > maintained per-sched_dl_entity (i.e. per-task) `dl_runtime/dl_deadline` > (dl_density). > > cap_scale(dl_deadline, cap) >= dl_runtime > > dl_deadline * cap >> SCHED_CAPACITY_SHIFT >= dl_runtime > > cap >= dl_runtime << SCHED_CAPACITY_SHIFT / dl_deadline > > with BW_SHIFT = 2 x SCHED_CAPACITY_SHIFT > > cap >= (dl_runtime << BW_SHIFT / dl_deadline) >> SCHED_CAPACITY_SHIFT > > cap >= dl_density >> SCHED_CAPACITY_SHIFT > > __sched_setscheduler()->__checkparam_dl() ensures that the 2 corner > cases (if conditions) `runtime == RUNTIME_INF (-1)` and `period == 0` > of to_ratio(deadline, runtime) are not met when setting dl_density in > __sched_setscheduler()-> __setscheduler_params()->__setparam_dl(). > > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > --- > kernel/sched/sched.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 79f65a6799c6..555f58d6c3a6 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -324,15 +324,15 @@ struct dl_bw { > * Verify the fitness of task @p to run on @cpu taking into account the > * CPU original capacity and the runtime/deadline ratio of the task. > * > - * The function will return true if the CPU original capacity of the > - * @cpu scaled by SCHED_CAPACITY_SCALE >= runtime/deadline ratio of the > - * task and false otherwise. > + * The function will return true if the original capacity of @cpu is > + * greater than or equal to task's deadline density right shifted by > + * SCHED_CAPACITY_SHIFT and false otherwise. > */ > static inline bool dl_task_fits_capacity(struct task_struct *p, int cpu) > { > unsigned long cap = arch_scale_cpu_capacity(cpu); > > - return cap_scale(p->dl.dl_deadline, cap) >= p->dl.dl_runtime; > + return cap >= p->dl.dl_density >> SCHED_CAPACITY_SHIFT;
There is no direct relation between BW_SHIFT and SCHED_CAPACITY_SHIFT and we can change one without modifying the other.
Should you use (BW_SHIFT-SCHED_CAPACITY_SHIFT) instead of SCHED_CAPACITY_SHIFT ?
> } > > extern void init_dl_bw(struct dl_bw *dl_b); > -- > 2.25.1 >
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