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

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

quoted

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

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?