[PATCH] nohz: Fix ondemand governor not always ramping up on 100% load.

From: Arve HjÃnnevÃg
Date: Sat May 30 2009 - 01:00:38 EST


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 HjÃnnevÃg <arve@xxxxxxxxxxx>
---
kernel/time/tick-sched.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index d3f1ef4..4012da6 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -222,7 +222,6 @@ void tick_nohz_stop_sched_tick(int inidle)

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
@@ -242,6 +241,7 @@ void tick_nohz_stop_sched_tick(int inidle)
if (!inidle && !ts->inidle)
goto end;

+ now = tick_nohz_start_idle(ts);
ts->inidle = 1;

if (need_resched())
--
1.6.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/