Re: [PATCH v4 02/16] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups

Patrick Bellasi
2018-09-12T10:32:09Z

Hi Suren,

On 08-Sep 16:47, Suren Baghdasaryan wrote:

[...]

> > + * A clamp group is not free if there is at least one SE which is sing a clamp
>
> typo in the sentence

Right, s/is sing/is using/

+1

[...]

> > +static int
> > +uclamp_group_find(int clamp_id, unsigned int clamp_value)
> > +{
> > + struct uclamp_map *uc_map = &uclamp_maps[clamp_id][0];
> > + int free_group_id = UCLAMP_NOT_VALID;
> > + unsigned int group_id = 0;
> > +
> > + for ( ; group_id <= CONFIG_UCLAMP_GROUPS_COUNT; ++group_id) {
> > + /* Keep track of first free clamp group */
> > + if (uclamp_group_available(clamp_id, group_id)) {
> > + if (free_group_id == UCLAMP_NOT_VALID)
> > + free_group_id = group_id;
> > + continue;
> > + }
>
> Not a big improvement but reordering the two conditions in this loop
> would avoid finding and recording free_group_id if the very first
> group is the one we are looking for.

Right, indeed with:

uclamp_group_put()
uclamp_group_reset()
uclamp_group_init()

we always ensure that:

uc_map[group_id].value == UCLAMP_NOT_VALID

for free groups. Thus, it should be safe to swap this two checks and
we likely save few instructions for a likely common case of non
clamped tasks.

+1

I'll also get the chance to remove the two simple comments. ;)

> > + /* Return index of first group with same clamp value */
> > + if (uc_map[group_id].value == clamp_value)
> > + return group_id;
> > + }
> > +
> > + if (likely(free_group_id != UCLAMP_NOT_VALID))
> > + return free_group_id;
> > +
> > + return -ENOSPC;
> > +}

[...]

> > +static inline void uclamp_group_put(int clamp_id, int group_id)

> Is the size and the number of invocations of this function small
> enough for inlining? Same goes for uclamp_group_get() and especially
> for __setscheduler_uclamp().

Right... yes, we could let the scheduler do its job and remove inline
from these functions... at least for those not in the critical path.

+1

[...]

> > + if (likely(uc_map[group_id].se_count))
> > + uc_map[group_id].se_count -= 1;
> > +#ifdef SCHED_DEBUG
> > + else {
>
> nit: no need for braces
>
> > + WARN(1, "invalid SE clamp group [%d:%d] refcount\n",
> > + clamp_id, group_id);

Since the above statement is multi-line, we actually need it for code
code-style requirements.

> > + }
> > +#endif

[...]

> > +static void uclamp_fork(struct task_struct *p, bool reset)
> > +{
> > + int clamp_id;
> > +
> > + if (unlikely(!p->sched_class->uclamp_enabled))
> > + return;
> > +
> > + for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
> > + int next_group_id = p->uclamp[clamp_id].group_id;
> > + struct uclamp_se *uc_se = &p->uclamp[clamp_id];
>
> Might be easier to read if after the above assignment you use
> uc_se->xxx instead of p->uclamp[clamp_id].xxx in the code below.

Yes, that's actually the intent of the above assigmenet... but I've
forgot a couple of usages! +1

> > +
> > + if (unlikely(reset)) {
> > + next_group_id = 0;
> > + p->uclamp[clamp_id].value = uclamp_none(clamp_id);
> > + }
> > +
> > + p->uclamp[clamp_id].group_id = UCLAMP_NOT_VALID;
> > + uclamp_group_get(clamp_id, next_group_id, uc_se,
> > + p->uclamp[clamp_id].value);
> > + }
> > +}

[...]

> Thanks,
> Suren.

Cheers,
Patrick

--
#include <best/regards.h>

Patrick Bellasi