Re: [PATCH v7 01/15] sched/core: uclamp: Add CPU's clamp buckets refcounting

[Peter Zijlstra]

On Fri, Feb 08, 2019 at 10:05:40AM +0000, Patrick Bellasi wrote:
> +static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
> +{
> +     return clamp_value / UCLAMP_BUCKET_DELTA;
> +}
> +
> +static inline unsigned int uclamp_bucket_value(unsigned int clamp_value)
> +{
> +     return UCLAMP_BUCKET_DELTA * uclamp_bucket_id(clamp_value);

        return clamp_value - (clamp_value % UCLAMP_BUCKET_DELTA);

might generate better code; just a single division, instead of a div and
mult.

> +}
> +
> +static inline unsigned int uclamp_none(int clamp_id)
> +{
> +     if (clamp_id == UCLAMP_MIN)
> +             return 0;
> +     return SCHED_CAPACITY_SCALE;
> +}
> +
> +static inline void uclamp_rq_update(struct rq *rq, unsigned int clamp_id)
> +{
> +     struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
> +     unsigned int max_value = uclamp_none(clamp_id);
> +     unsigned int bucket_id;
> +
> +     /*
> +      * Both min and max clamps are MAX aggregated, thus the topmost
> +      * bucket with some tasks defines the rq's clamp value.
> +      */
> +     bucket_id = UCLAMP_BUCKETS;
> +     do {
> +             --bucket_id;
> +             if (!rq->uclamp[clamp_id].bucket[bucket_id].tasks)
> +                     continue;
> +             max_value = bucket[bucket_id].value;
> +             break;

If you flip the if condition the code will be nicer.

> +     } while (bucket_id);

But you can also use a for loop:

        for (i = UCLAMP_BUCKETS-1; i>=0; i--) {
                if (rq->uclamp[clamp_id].bucket[i].tasks) {
                        max_value = bucket[i].value;
                        break;
                }
        }

> +     WRITE_ONCE(rq->uclamp[clamp_id].value, max_value);
> +}