cpufreq: schedutil: Add iowait boosting

Modify the schedutil cpufreq governor to boost the CPU
frequency if the SCHED_CPUFREQ_IOWAIT flag is passed to
it via cpufreq_update_util().

If that happens, the frequency is set to the maximum during
the first update after receiving the SCHED_CPUFREQ_IOWAIT flag
and then the boost is reduced by half during each following update.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Looks-good-to: Steve Muckle <smuckle@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

kernel/sched/cpufreq_schedutil.c

@@ -47,11 +47,13 @@ struct sugov_cpu {
 	struct sugov_policy *sg_policy;
 
 	unsigned int cached_raw_freq;
+	unsigned long iowait_boost;
+	unsigned long iowait_boost_max;
+	u64 last_update;
 
 	/* The fields below are only needed when sharing a policy. */
 	unsigned long util;
 	unsigned long max;
-	u64 last_update;
 	unsigned int flags;
 };
 
@@ -155,6 +157,36 @@ static void sugov_get_util(unsigned long *util, unsigned long *max)
 	*max = cfs_max;
 }
 
+static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
+				   unsigned int flags)
+{
+	if (flags & SCHED_CPUFREQ_IOWAIT) {
+		sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
+	} else if (sg_cpu->iowait_boost) {
+		s64 delta_ns = time - sg_cpu->last_update;
+
+		/* Clear iowait_boost if the CPU apprears to have been idle. */
+		if (delta_ns > TICK_NSEC)
+			sg_cpu->iowait_boost = 0;
+	}
+}
+
+static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, unsigned long *util,
+			       unsigned long *max)
+{
+	unsigned long boost_util = sg_cpu->iowait_boost;
+	unsigned long boost_max = sg_cpu->iowait_boost_max;
+
+	if (!boost_util)
+		return;
+
+	if (*util * boost_max < *max * boost_util) {
+		*util = boost_util;
+		*max = boost_max;
+	}
+	sg_cpu->iowait_boost >>= 1;
+}
+
 static void sugov_update_single(struct update_util_data *hook, u64 time,
 				unsigned int flags)
 {
@@ -164,13 +196,17 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
 	unsigned long util, max;
 	unsigned int next_f;
 
+	sugov_set_iowait_boost(sg_cpu, time, flags);
+	sg_cpu->last_update = time;
+
 	if (!sugov_should_update_freq(sg_policy, time))
 		return;
 
 	if (flags & SCHED_CPUFREQ_RT_DL) {
 		next_f = policy->cpuinfo.max_freq;
 	} else {
 		sugov_get_util(&util, &max);
+		sugov_iowait_boost(sg_cpu, &util, &max);
 		next_f = get_next_freq(sg_cpu, util, max);
 	}
 	sugov_update_commit(sg_policy, time, next_f);
@@ -189,6 +225,8 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu,
 	if (flags & SCHED_CPUFREQ_RT_DL)
 		return max_f;
 
+	sugov_iowait_boost(sg_cpu, &util, &max);
+
 	for_each_cpu(j, policy->cpus) {
 		struct sugov_cpu *j_sg_cpu;
 		unsigned long j_util, j_max;
@@ -203,12 +241,13 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu,
 		 * frequency update and the time elapsed between the last update
 		 * of the CPU utilization and the last frequency update is long
 		 * enough, don't take the CPU into account as it probably is
-		 * idle now.
+		 * idle now (and clear iowait_boost for it).
 		 */
 		delta_ns = last_freq_update_time - j_sg_cpu->last_update;
-		if (delta_ns > TICK_NSEC)
+		if (delta_ns > TICK_NSEC) {
+			j_sg_cpu->iowait_boost = 0;
 			continue;
-
+		}
 		if (j_sg_cpu->flags & SCHED_CPUFREQ_RT_DL)
 			return max_f;
 
@@ -218,6 +257,8 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu,
 			util = j_util;
 			max = j_max;
 		}
+
+		sugov_iowait_boost(j_sg_cpu, &util, &max);
 	}
 
 	return get_next_freq(sg_cpu, util, max);
@@ -238,6 +279,8 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
 	sg_cpu->util = util;
 	sg_cpu->max = max;
 	sg_cpu->flags = flags;
+
+	sugov_set_iowait_boost(sg_cpu, time, flags);
 	sg_cpu->last_update = time;
 
 	if (sugov_should_update_freq(sg_policy, time)) {
@@ -470,6 +513,8 @@ static int sugov_start(struct cpufreq_policy *policy)
 			sg_cpu->flags = SCHED_CPUFREQ_RT;
 			sg_cpu->last_update = 0;
 			sg_cpu->cached_raw_freq = 0;
+			sg_cpu->iowait_boost = 0;
+			sg_cpu->iowait_boost_max = policy->cpuinfo.max_freq;
 			cpufreq_add_update_util_hook(cpu, &sg_cpu->update_util,
 						     sugov_update_shared);
 		} else {