Thread (21 messages) 21 messages, 9 authors, 2014-01-24

Re: [ANNOUNCE] 3.12.6-rt9

From: Muli Baron <hidden>
Date: 2014-01-21 06:39:23

On 21/1/2014 04:17, Steven Rostedt wrote:
quoted hunk ↗ jump to hunk
On Sat, 18 Jan 2014 04:15:29 +0100
Mike Galbraith [off-list ref] wrote:

quoted
quoted
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@goodmis.org>
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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