On 13-Mar 14:40, Peter Zijlstra wrote:

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

quoted

+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.

quoted

+}
+
+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.

quoted

+	} 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.

quoted

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

-- 
#include <best/regards.h>

Patrick Bellasi