On 21/1/2014 04:17, Steven Rostedt wrote:
On Sat, 18 Jan 2014 04:15:29 +0100
Mike Galbraith <bitbucket@xxxxxxxxx> wrote:
So you also have the timers-do-not-raise-softirq-unconditionally.patch?
People have been complaining that the latest 3.12-rt does not boot on
intel i7 boxes. And by reverting this patch, it boots fine.
I happen to have a i7 box to test on, and sure enough, the latest
3.12-rt locks up on boot and reverting the
timers-do-not-raise-softirq-unconditionally.patch, it boots fine.
Looking into it, I made this small update, and the box boots. Seems
checking "active_timers" is not enough to skip raising softirqs. I
haven't looked at why yet, but I would like others to test this patch
too.
I'll leave why this lets i7 boxes boot as an exercise for Thomas ;-)
-- Steve
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
diff --git a/kernel/timer.c b/kernel/timer.c
index 46467be..8212c10 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1464,13 +1464,11 @@ void run_local_timers(void)
raise_softirq(TIMER_SOFTIRQ);
return;
}
- if (!base->active_timers)
- goto out;
/* Check whether the next pending timer has expired */
if (time_before_eq(base->next_timer, jiffies))
raise_softirq(TIMER_SOFTIRQ);
-out:
+
rt_spin_unlock_after_trylock_in_irq(&base->lock);
}
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While this might fix booting on i7 machines it kinds of defeats the
original purpose of this patch, which was to let NO_HZ_FULL work
properly with threaded interrupts. With the active_timers check removed
the timer interrupt keeps firing even though there is only one task
running on a specific processor, since it can't shut down the tick
because the ksoftirqd thread keeps getting scheduled (see the previous
thread "CONFIG_NO_HZ_FULL + CONFIG_PREEMPT_RT_FULL = nogo" for the full
discussion).
-- Muli
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