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ANDROID: sched/fair: Cap transient util in stune

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boosted_cpu_util() sums the CFS and RT util signals before they are used
for frequency selection. While the util_avg signals are in sync,
util_est prevents cpu_util_cfs() from decreasing when a CFS task is
preempted by RT.

This util_est behaviour is beneficial in many scenarios, but it can
cause the sum of rt_util and cfs_util to go above SCHED_CAPACITY_SCALE.
Although benign, this transient value appears in the stune tracepoints,
and can cause confusion.

Work around the problem by capping the util sum to SCHED_CAPACITY_SCALE.

Bug: 120440300
Change-Id: I2be6eb157af86024e52ae11715f5637c77b201a3
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
This commit is contained in:
Quentin Perret
2019-08-16 10:30:58 +01:00
parent b1e96f1650
commit 8e9d3d0740
1 changed files with 2 additions and 1 deletions
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3
kernel/sched/fair.c
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@@ -5922,7 +5922,8 @@ schedtune_task_margin(struct task_struct *task)
unsigned long
boosted_cpu_util(int cpu, unsigned long other_util)
{
unsigned long util = cpu_util_cfs(cpu_rq(cpu)) + other_util;
unsigned long util = min_t(unsigned long, SCHED_CAPACITY_SCALE,
cpu_util_cfs(cpu_rq(cpu)) + other_util);
long margin = schedtune_cpu_margin(util, cpu);
trace_sched_boost_cpu(cpu, util, margin);