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From:   Qais Yousef <qyousef@layalina.io>
To:     Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        Lukasz Luba <lukasz.luba@arm.com>, Wei Wang <wvw@google.com>,
        Rick Yiu <rickyiu@google.com>,
        Chung-Kai Mei <chungkai@google.com>,
        Qais Yousef <qyousef@layalina.io>
Subject: [PATCH v2 3/8] sched/pelt: Add a new function to approximate the future util_avg value
Date:   Fri,  8 Dec 2023 00:23:37 +0000
Message-Id: <20231208002342.367117-4-qyousef@layalina.io>
In-Reply-To: <20231208002342.367117-1-qyousef@layalina.io>
References: <20231208002342.367117-1-qyousef@layalina.io>
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Given a util_avg value, the new function will return the future one
given a runtime delta.

This will be useful in later patches to help replace some magic margins
with more deterministic behavior.

Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
---
 kernel/sched/pelt.c  | 22 +++++++++++++++++++++-
 kernel/sched/sched.h |  2 ++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index 63b6cf898220..81555a8288be 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -466,4 +466,24 @@ int update_irq_load_avg(struct rq *rq, u64 running)
 
 	return ret;
 }
-#endif
+#endif /* CONFIG_HAVE_SCHED_AVG_IRQ */
+
+/*
+ * Approximate the new util_avg value assuming an entity has continued to run
+ * for @delta us.
+ */
+unsigned long approximate_util_avg(unsigned long util, u64 delta)
+{
+	struct sched_avg sa = {
+		.util_sum = util * PELT_MIN_DIVIDER,
+		.util_avg = util,
+	};
+
+	if (unlikely(!delta))
+		return util;
+
+	accumulate_sum(delta, &sa, 1, 0, 1);
+	___update_load_avg(&sa, 0);
+
+	return sa.util_avg;
+}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0da3425200b1..7e5a86a376f8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3002,6 +3002,8 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
 				 unsigned long min,
 				 unsigned long max);
 
+unsigned long approximate_util_avg(unsigned long util, u64 delta);
+
 /*
  * DVFS decision are made at discrete points. If CPU stays busy, the util will
  * continue to grow, which means it could need to run at a higher frequency
-- 
2.34.1