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    SubjectRe: [PATCH v7 01/15] sched/core: uclamp: Add CPU's clamp buckets refcounting
    On 13-Mar 14:40, Peter Zijlstra wrote:
    > 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.

    Wondering if compilers cannot do these optimizations... but yes, looks
    cool and will do it in v8, thanks.

    > > +}
    > > +
    > > +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;
    > }
    > }

    Yes, the for looks better, but perhaps like that:

    unsigned int bucket_id = UCLAMP_BUCKETS;

    /*
    * Both min and max clamps are MAX aggregated, thus the topmost
    * bucket with some tasks defines the rq's clamp value.
    */
    for (; bucket_id >= 0; --bucket_id) {
    if (!bucket[bucket_id].tasks)
    continue;
    max_value = bucket[bucket_id].value;
    break;
    }

    ... just to save a {} block.


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

    --
    #include <best/regards.h>

    Patrick Bellasi

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