linux-kernel - Re: [PATCH 2/2] timers: Fix removed self-IPI on global timer's enqueue in nohz

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Date: Tue, 2 Apr 2024 09:47:37 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [PATCH 2/2] timers: Fix removed self-IPI on global timer's
 enqueue in nohz_full

On Mon, Apr 01, 2024 at 05:04:10PM -0700, Paul E. McKenney wrote:
> On Mon, Apr 01, 2024 at 11:56:36PM +0200, Frederic Weisbecker wrote:
> > Le Mon, Apr 01, 2024 at 02:26:25PM -0700, Paul E. McKenney a écrit :
> > > > > _ The RCU CPU Stall report. I strongly suspect the cause is the hrtimer
> > > > >   enqueue to an offline CPU. Let's solve that and we'll see if it still
> > > > >   triggers.
> > > > 
> > > > Sounds like a plan!
> > > 
> > > Just checking in on this one.  I did reproduce your RCU CPU stall report
> > > and also saw a TREE03 OOM that might (or might not) be related.  Please
> > > let me know if hammering TREE03 harder or adding some debug would help.
> > > Otherwise, I will assume that you are getting sufficient bug reports
> > > from your own testing to be getting along with.
> > 
> > Hehe, there are a lot indeed :-)
> > 
> > So there has been some discussion on CPUSET VS Hotplug, as a problem there
> > is likely the cause of the hrtimer warning you saw, which in turn might
> > be the cause of the RCU stalls.
> > 
> > Do you always see the hrtimer warning along the RCU stalls? Because if so, this
> > might help:
> > https://lore.kernel.org/lkml/20240401145858.2656598-1-longman@redhat.com/T/#m1bed4d298715d1a6b8289ed48e9353993c63c896
> 
> Not always, but why not give it a shot?

And no failures, though I would need to run much longer for this to
mean much.  These were wide-spectrum tests, so my next step will be to
run only TREE03 and TREE07.

							Thanx, Paul