linux-kernel - [PATCH 49/70] cpufreq: interactive: avoid underflow on active time calculation

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Date:	Tue, 27 Oct 2015 18:30:37 +0100
From:	Bálint Czobor <czoborbalint@...il.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Minsung Kim <ms925.kim@...sung.com>,
	Bálint Czobor <czoborbalint@...il.com>
Subject: [PATCH 49/70] cpufreq: interactive: avoid underflow on active time calculation

From: Minsung Kim <ms925.kim@...sung.com>

Check for idle time delta less than elapsed time delta, avoid
underflow computing active time.

Change-Id: I3e4c6ef1ad794eec49ed379c0c50fa727fd6ad28
Signed-off-by: Minsung Kim <ms925.kim@...sung.com>
Signed-off-by: Bálint Czobor <czoborbalint@...il.com>
---
 drivers/cpufreq/cpufreq_interactive.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cpufreq_interactive.c b/drivers/cpufreq/cpufreq_interactive.c
index b4d12b2..7303f50 100644
--- a/drivers/cpufreq/cpufreq_interactive.c
+++ b/drivers/cpufreq/cpufreq_interactive.c
@@ -325,7 +325,12 @@ static u64 update_load(int cpu)
 	now_idle = get_cpu_idle_time(cpu, &now);
 	delta_idle = (unsigned int)(now_idle - pcpu->time_in_idle);
 	delta_time = (unsigned int)(now - pcpu->time_in_idle_timestamp);
-	active_time = delta_time - delta_idle;
+
+	if (delta_time <= delta_idle)
+		active_time = 0;
+	else
+		active_time = delta_time - delta_idle;
+
 	pcpu->cputime_speedadj += active_time * pcpu->policy->cur;
 
 	pcpu->time_in_idle = now_idle;
-- 
1.7.9.5

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