linux-kernel - Re: [PATCH v3 00/10] Add tegra30 support for secondary cores

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Message-ID: <20120229154229.GL12917@tbergstrom-lnx.Nvidia.com>
Date:	Wed, 29 Feb 2012 17:42:29 +0200
From:	Peter De Schrijver <pdeschrijver@...dia.com>
To:	Stephen Warren <swarren@...dia.com>
CC:	Colin Cross <ccross@...roid.com>, Olof Johansson <olof@...om.net>,
	Russell King <linux@....linux.org.uk>,
	Gary King <gking@...dia.com>, Arnd Bergmann <arnd@...db.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 00/10] Add tegra30 support for secondary cores

On Wed, Feb 15, 2012 at 10:27:43PM +0100, Stephen Warren wrote:
> Peter De Schrijver wrote at Thursday, February 09, 2012 4:48 PM:
> > This patchset introduces support for secondary cores on tegra30. It also
> > introduces some functions for the flowcontroller and adds basic support for
> > tegra30 powerdomains.
> 
> The code looks fine to me. I do notice the following when running
> "shutdown -h now":
> 
> [   27.762124] SMP: failed to stop secondary CPUs
> 
> So, this patch series makes the secondary cores boot OK, but not shut
> down it appears. Is that expected? It's probably something we can fix
> with a following on patch rather than re-spinning this series though?
> 

I spent some more time looking at this. It appears that nr_online_cpus isn't
always updated properly. I added an extra pr_warn() when the failure happens
and I got:

[   22.369815] Restarting system.
[   23.506792] SMP: failed to stop secondary CPUs
[   23.511535] running on CPU: 3, still online: 2, mask: 8

I also did some function tracing and all CPUs besides the one initiating the
halt reach platform_cpu_kill() about 50us after sending the IPIs to stop them.
The set_cpu_online() call in ipi_cpu_stop() should update nr_online_cpus, but
somehow this doesn't always happen. Any insight on what might be going on?

Instrumentation patch attached.

Cheers,

Peter.


View attachment "0001-ARM-debugging-smp_send_stop.patch" of type "text/x-diff" (1190 bytes)