[PATCH 2/3] sched/pelt: Add a new function to approximate runtime to reach given util

[Qais Yousef]

It is basically the ramp-up time from 0 to a given value. Will be used
later to help remove magic margins with something more deterministic.

Signed-off-by: Qais Yousef <qyousef@xxxxxxxxxxx>
---
 kernel/sched/pelt.c  | 21 +++++++++++++++++++++
 kernel/sched/sched.h |  1 +
 2 files changed, 22 insertions(+)

diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index 81555a8288be..00a1b9c1bf16 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -487,3 +487,24 @@ unsigned long approximate_util_avg(unsigned long util, u64 delta)
 
 	return sa.util_avg;
 }
+
+/*
+ * Approximate the required amount of runtime in ms required to reach @util.
+ */
+u64 approximate_runtime(unsigned long util)
+{
+	struct sched_avg sa = {};
+	u64 delta = 1024; // period = 1024 = ~1ms
+	u64 runtime = 0;
+
+	if (unlikely(!util))
+		return runtime;
+
+	while (sa.util_avg < util) {
+		accumulate_sum(delta, &sa, 1, 0, 1);
+		___update_load_avg(&sa, 0);
+		runtime++;
+	}
+
+	return runtime;
+}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1c15ff5ef5a4..d078e6481bd0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3003,6 +3003,7 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
 				 unsigned long max);
 
 unsigned long approximate_util_avg(unsigned long util, u64 delta);
+u64 approximate_runtime(unsigned long util);
 
 /*
  * Verify the fitness of task @p to run on @cpu taking into account the
-- 
2.34.1