linux-kernel - Re: [PATCH] x86: Fix thermal throttling reporting after kexec

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Message-ID: <20151001172737.GC26924@tassilo.jf.intel.com>
Date:	Thu, 1 Oct 2015 10:27:37 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Fix thermal throttling reporting after kexec

On Thu, Oct 01, 2015 at 02:15:54PM +0200, Thomas Gleixner wrote:
> On Thu, 24 Sep 2015, Andi Kleen wrote:
> > The per CPU thermal vector init code checks if the thermal
> > vector is already installed and complains and bails out if
> > it is.
> > 
> > This happens after kexec, as kernel shut down does
> > not clear the thermal vector APIC register.
> 
> So the obvious question is, why don't we do that.

It wouldn't help if the previous kernel is some older kernel.

> 
> > Just remove the check. I checked the code and there's
> > no valid code paths where the thermal init code for a CPU
> > could be called multiple times.
> 
> I'm not against removing that check as it does not really add value,
> but we still should clear the APIC register at shut down, right?

The vector register is really harmless by itself and apart from
bogus checking it's not really affecting anyone. It may make
more sense to disable thermal reporting on shut down though.

I can add that, although it would only be useful for the more
theoretical case when you boot non Linux after kexec (as normal
Linux always reenables it anyways)

But the check should still be removed imho.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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