linux-kernel - [PATCH RFC 5/8] sched/cpufreq_schedutil: always consider all CPUs when deciding next freq

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Message-Id: <20170523085351.18586-6-juri.lelli@arm.com>
Date:   Tue, 23 May 2017 09:53:48 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     peterz@...radead.org, mingo@...hat.com, rjw@...ysocki.net,
        viresh.kumar@...aro.org
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        tglx@...utronix.de, vincent.guittot@...aro.org,
        rostedt@...dmis.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org, tkjos@...roid.com,
        joelaf@...gle.com, andresoportus@...gle.com,
        morten.rasmussen@....com, dietmar.eggemann@....com,
        patrick.bellasi@....com, juri.lelli@....com,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: [PATCH RFC 5/8] sched/cpufreq_schedutil: always consider all CPUs when deciding next freq

No assumption can be made upon the rate at which frequency updates get
triggered, as there are scheduling policies (like SCHED_DEADLINE) which
don't trigger them so frequently.

Remove such assumption from the code, by always considering
SCHED_DEADLINE utilization signal as not stale.

Signed-off-by: Juri Lelli <juri.lelli@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Luca Abeni <luca.abeni@...tannapisa.it>
Cc: Claudio Scordino <claudio@...dence.eu.com>
---
Changes from RFD
 - discard CFS contribution only as stale (as suggested by Rafael)
---
 kernel/sched/cpufreq_schedutil.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index f930cec4c3d4..688bd11c2641 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -259,17 +259,22 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
 		s64 delta_ns;
 
 		/*
-		 * If the CPU utilization was last updated before the previous
-		 * 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 (and clear iowait_boost for it).
+		 * If the CFS CPU utilization was last updated before the
+		 * previous frequency update and the time elapsed between the
+		 * last update of the CPU utilization and the last frequency
+		 * update is long enough, reset iowait_boost and util_cfs, as
+		 * they are now probably stale. However, still consider the
+		 * CPU contribution if it has some DEADLINE utilization
+		 * (util_dl).
 		 */
 		delta_ns = time - j_sg_cpu->last_update;
 		if (delta_ns > TICK_NSEC) {
 			j_sg_cpu->iowait_boost = 0;
-			continue;
+			j_sg_cpu->util_cfs = 0;
+			if (j_sg_cpu->util_dl == 0)
+				continue;
 		}
+
 		if (j_sg_cpu->flags & SCHED_CPUFREQ_RT)
 			return policy->cpuinfo.max_freq;
 
-- 
2.11.0