Re: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization update flags

Currently the schedutil governor overwrites the sg_cpu->flags field on
every call to the utilization handler. It was pretty good as the initial
implementation of utilization handlers, there are several drawbacks
though.

The biggest drawback is that the sg_cpu->flags field doesn't always
represent the correct type of tasks that are enqueued on a CPU's rq. For
example, if a fair task is enqueued while a RT or DL task is running, we
will overwrite the flags with value 0 and that may take the CPU to lower
OPPs unintentionally. There can be other corner cases as well which we
aren't aware of currently.

This patch changes the current implementation to keep track of all the
task types that are currently enqueued to the CPUs rq. A new flag: CLEAR
is introduced and is set by the scheduling classes when their last task
is dequeued. When the CLEAR flag bit is set, the schedutil governor resets
all the other flag bits that are present in the flags parameter. For
now, the util update handlers return immediately if they were called to
clear the flag.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 include/linux/sched/cpufreq.h    |  7 ++++++-
 kernel/sched/cpufreq_schedutil.c | 21 ++++++++++++++++++---
 kernel/sched/deadline.c          |  4 ++++
 kernel/sched/fair.c              |  8 ++++++--
 kernel/sched/rt.c                |  4 ++++
 5 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
index d1ad3d825561..6f6641e61236 100644
--- a/include/linux/sched/cpufreq.h
+++ b/include/linux/sched/cpufreq.h

@@ -8,10 +8,15 @@
  * Interface between cpufreq drivers and the scheduler:
  */

+#define SCHED_CPUFREQ_CLEAR    (1U << 31)