Re: [PATCH v4 7/7] cpufreq: schedutil: New governor based on scheduler utilization data

On Wednesday, March 16, 2016 06:35:41 PM Peter Zijlstra wrote:

On Wed, Mar 16, 2016 at 03:59:18PM +0100, Rafael J. Wysocki wrote:

quoted

+static unsigned int get_next_freq(struct cpufreq_policy *policy,
+				  unsigned long util, unsigned long max)
+{
+	unsigned int freq = arch_scale_freq_invariant() ?
+				policy->cpuinfo.max_freq : policy->cur;
+
+	return (freq + (freq >> 2)) * util / max;
+}
+
+static void sugov_update_single(struct update_util_data *hook, u64 time,
+				unsigned long util, unsigned long max)
+{
+	struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
+	struct sugov_policy *sg_policy = sg_cpu->sg_policy;
+	struct cpufreq_policy *policy = sg_policy->policy;
+	unsigned int next_f;
+
+	if (!sugov_should_update_freq(sg_policy, time))
+		return;
+
+	next_f = util <= max ?
+		get_next_freq(policy, util, max) : policy->cpuinfo.max_freq;

I'm not sure that is correct, would not something like this be more
accurate?

	if (util > max)
		util = max;
	next_f = get_next_freq(policy, util, max);

After all, if we clip util we will still only increment to the next freq
with our multiplication factor.

Hmm, or was this meant to deal with the DL/RT stuff?

Yes, it was.

Would then not something like:

	/* ULONG_MAX is used to force max_freq for Real-Time policies */
	if (util == ULONG_MAX) {
		next_f = policy->cpuinfo.max_freq;
	} else {
		if (util > max)

That cannot happen given the way CFS deals with max before passing it
to cpufreq_update_util().

			util = max;
		next_f = get_next_freq(policy, util, max);
	}

Be clearer?

quoted

+	sugov_update_commit(sg_policy, time, next_f);
+}

So essentially I can replace the util > max check with the util == ULONG_MAX one
(here and in some other places) if that helps to understand the code, but
functionally that won't change anything.