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

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Date:	Thu, 1 Oct 2015 23:41:02 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <ak@...ux.intel.com>
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, 1 Oct 2015, Andi Kleen wrote:
> 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.

I know.
 
> > 
> > > 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)

I see it under the correctness aspect. Mop up before you shut down.
 
> But the check should still be removed imho.

As I said before: I have no objections against that.

Thanks,

	tglx
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