linux-kernel - Re: smp_call_function

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Date:	Wed, 1 Apr 2015 09:32:36 -0500
From:	Chris J Arges <chris.j.arges@...onical.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rafael David Tinoco <inaddy@...ntu.com>,
	Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gema Gomez <gema.gomez-solano@...onical.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: smp_call_function_single lockups

On Tue, Mar 31, 2015 at 04:07:32PM -0700, Linus Torvalds wrote:
> On Tue, Mar 31, 2015 at 3:23 PM, Chris J Arges
> <chris.j.arges@...onical.com> wrote:
> >
> > I had a few runs with your patch plus modifications, and got the following
> > results (modified patch inlined below):
> 
> Ok, thanks.
> 
> > [   14.423916] ack_APIC_irq: vector = d1, irq = ffffffff
> > [  176.060005] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [qemu-system-x86:1630]
> >
> > [   17.995298] ack_APIC_irq: vector = d1, irq = ffffffff
> > [  182.993828] ack_APIC_irq: vector = e1, irq = ffffffff
> > [  202.919691] ack_APIC_irq: vector = 22, irq = ffffffff
> > [  484.132006] NMI watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [qemu-system-x86:1586]
> >
> > [   15.592032] ack_APIC_irq: vector = d1, irq = ffffffff
> > [  304.993490] ack_APIC_irq: vector = e1, irq = ffffffff
> > [  315.174755] ack_APIC_irq: vector = 22, irq = ffffffff
> > [  360.108007] NMI watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [ksmd:26]
> .. snip snip ..
> 
> So yeah, that's VECTOR_UNDEFINED, and while it could happen as part of
> irq setup, I'm not seeing that being something that your load should
> trigger.
> 
> It could also obviously just be the vector being somehow corrupted,
> either due to crazy hardware or software.
> 
> But quite frankly, the most likely reason is that whole irq vector movement.
> 
> Especially since it sounds from your other email that when you apply
> Ingo's patches, the ack_APIC_irq warnings go away. Is that correct? Or
> did you just grep for "move" in the messages?
> 
> If you do get both movement messages (from Info's patch) _and_ the
> ack_APIC_irq warnings (from mine), it would be interesting to see if
> the vectors line up somehow..
> 
>                      Linus
> 

Linus,

I included the full patch in reply to Ingo's email, and when running with that
I no longer get the ack_APIC_irq WARNs.

My next homework assignments are:
- Testing with irqbalance disabled
- Testing w/ the appropriate dump_stack() in Ingo's patch
- L0 testing

Thanks,
--chris


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