Hi Peter,
On Fri, 24 Mar 2017 15:00:15 +0100
Peter Zijlstra <pet...@infradead.org> wrote:
> On Fri, Mar 24, 2017 at 04:52:58AM +0100, luca abeni wrote:
>
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 20c62e7..efa88eb 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -6716,6 +6716,12 @@ static void sched_dl_do_global(void)
> > raw_spin_unlock_irqrestore(&dl_b->lock, flags);
> >
> > rcu_read_unlock_sched();
> > + if (dl_b->bw == -1)
> > + cpu_rq(cpu)->dl.deadline_bw_inv = 1 << 8;
> > + else
> > + cpu_rq(cpu)->dl.deadline_bw_inv =
> > + to_ratio(global_rt_runtime(),
> > + global_rt_period()) >>
> > 12;
>
> Coding style requires braces here (on both legs of the condition)..
Sorry about this; checkpatch did not complain and I did not check the
coding rules. I'll add the braces.
> Also, I find deadline_bw_inv an awkward name; would something like
> bw_ratio or so be more accurate?
I am not good at finding names :)
(I used "deadline_bw_inv" because it represents the inverse of the
deadline tasks bandwidth")
I'll change the name in bw_ratio or something better (suggestions?)
> > + if (global_rt_runtime() == RUNTIME_INF)
> > + dl_rq->deadline_bw_inv = 1 << 8;
> > + else
> > + dl_rq->deadline_bw_inv =
> > + to_ratio(global_rt_runtime(),
> > global_rt_period()) >> 12;
>
> That's almost the same code; do we want a helper function?
OK, I'll look at this.
> > u64 grub_reclaim(u64 delta, struct rq *rq)
> > {
> > + return (delta * rq->dl.running_bw *
> > rq->dl.deadline_bw_inv) >> 20 >> 8; }
>
> At which point we might want a note about how this doesn't overflow I
> suppose.
I'll add it on Monday.
>
> Also:
>
> delta *= rq->dl.running_bw;
> delta *= rq->dl.bw_ratio;
> delta >>= 20 + 8;
>
> return delta;
>
> Might be more readable ?
>
> Alternatively:
>
> delta = (delta * rq->dl.running_bw) >> 8;
> delta = (delta * rq->dl.bw_ratio) >> 20;
>
> return delta;
>
> But I doubt we care about those extra 8 bit of space; delta should not
> be over 36 bits (~64 seconds) anyway I suppose.
I think the version with all the shifts after the multiplications is
more precise, right?
Thanks,
Luca
