On 13-Mar 14:08, Suren Baghdasaryan wrote:

On Wed, Mar 13, 2019 at 12:46 PM Peter Zijlstra [off-list ref] wrote:

quoted

On Wed, Mar 13, 2019 at 03:23:59PM +0000, Patrick Bellasi wrote:

quoted

On 13-Mar 15:09, Peter Zijlstra wrote:

quoted

On Fri, Feb 08, 2019 at 10:05:40AM +0000, Patrick Bellasi wrote:

quoted

quoted

quoted

+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);

That's 1024 for uclamp_max

quoted

+ 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;

but this will then _lower_ it. That's not a MAX aggregate.

For uclamp_max we want max_value=1024 when there are no active tasks,
which means: no max clamp enforced on CFS/RT "idle" cpus.

If instead there are active RT/CFS tasks then we want the clamp value
of the max group, which means: MAX aggregate active clamps.

That's what the code above does and the comment says.

That's (obviously) not how I read it... maybe something like:

static inline void uclamp_rq_update(struct rq *rq, unsigned int clamp_id)
{
        struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
        int i;

        /*
         * Since both min and max clamps are max aggregated, find the
         * top most bucket with tasks in.
         */
        for (i = UCLMAP_BUCKETS-1; i>=0; i--) {
                if (!bucket[i].tasks)
                        continue;
                return bucket[i].value;
        }

        /* No tasks -- default clamp values */
        return uclamp_none(clamp_id);
}

would make it clearer?

This way it's also more readable/obvious when it's used inside
uclamp_rq_dec_id, assuming uclamp_rq_update is renamed into smth like
get_max_rq_uclamp.

Rightm, I have now something like that:

---8<---
static inline unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id)
{
	struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
	int bucket_id;

	/*
	 * Since both min and max clamps are max aggregated, find the
	 * top most bucket with tasks in.
	 */
	for (bucket_id = UCLMAP_BUCKETS-1; bucket_id >= 0; bucket_id--) {
		if (!bucket[bucket_id].tasks)
			continue;
		return bucket[bucket_id].value;
	}

	/* No tasks -- default clamp value */
	return uclamp_none(clamp_id);
}

static inline void uclamp_rq_dec_id(struct task_struct *p, struct rq *rq,
				    unsigned int clamp_id)
{
        //...
	if (bucket->value >= rq_clamp) {
		/*
		 * Reset rq's clamp bucket value to its nominal value whenever
		 * there are anymore RUNNABLE tasks refcounting it.
		 */
		bucket->value = uclamp_bucket_nominal_value(rq_clamp);
		WRITE_ONCE(uc_rq->value, uclamp_rq_max_value(rq, clamp_id));
	}
}
---8<---

-- 
#include <best/regards.h>

Patrick Bellasi