The patch titled
time: nohz: fix ondemand governor not always ramping up on 100% load.
has been added to the -mm tree. Its filename is
time-nohz-fix-ondemand-governor-not-always-ramping-up-on-100%-load.patch
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------------------------------------------------------
Subject: time: nohz: fix ondemand governor not always ramping up on 100% load.
From: Arve Hjonnevag <arve@xxxxxxxxxxx>
On systems that perform the context switch with interrupts enabled (e.g.
ARM) get_cpu_idle_time_us could get stuck returning the last idle time
when the cpu is busy. If an interrupt occurs while switching to the idle
thread, and this interrupt wakes up a thread, need-resched will be set on
the idle thread, but since we have not finished switching to the idle
thread tick_nohz_stop_sched_tick will be called. (idle_cpu is true since
the head of the runqueue is the idle thread, but need_resched returns
false since we are still running in the context of the old thread)
Fix this by not calling tick_nohz_start_idle when returning from an
interrupt while the idle thread is in its schedule phase. (!ts->inidle)
Signed-off-by: Arve Hjonnevag <arve@xxxxxxxxxxx>
Cc: Brian Sewtland <swetland@xxxxxxxxxx>
Cc: Russell King <rmk@xxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/time/tick-sched.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN kernel/time/tick-sched.c~time-nohz-fix-ondemand-governor-not-always-ramping-up-on-100%-load kernel/time/tick-sched.c
--- a/kernel/time/tick-sched.c~time-nohz-fix-ondemand-governor-not-always-ramping-up-on-100%-load
+++ a/kernel/time/tick-sched.c
@@ -224,7 +224,6 @@ void tick_nohz_stop_sched_tick(int inidl
cpu = smp_processor_id();
ts = &per_cpu(tick_cpu_sched, cpu);
- now = tick_nohz_start_idle(ts);
/*
* If this cpu is offline and it is the one which updates
@@ -244,6 +243,7 @@ void tick_nohz_stop_sched_tick(int inidl
if (!inidle && !ts->inidle)
goto end;
+ now = tick_nohz_start_idle(ts);
ts->inidle = 1;
if (need_resched())
_
Patches currently in -mm which might be from arve@xxxxxxxxxxx are
linux-next.patch
time-nohz-fix-ondemand-governor-not-always-ramping-up-on-100%-load.patch
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