linux-kernel - Re: [PATCH] x86: Document the hotplug code is incompatible with x86 irq handling

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Message-Id: <200706012234.16882.rjw@sisk.pl>
Date:	Fri, 1 Jun 2007 22:34:15 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Robert Hancock <hancockr@...w.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	Neil Brown <neilb@...e.de>, Ingo Molnar <mingo@...e.hu>,
	Zwane Mwaikambo <zwane@...uxpower.ca>
Subject: Re: [PATCH] x86: Document the hotplug code is incompatible with x86 irq handling

On Friday, 1 June 2007 21:48, Eric W. Biederman wrote:
> "Rafael J. Wysocki" <rjw@...k.pl> writes:
> >> Cool.
> >> 
> >> My patch does not change the functionality of the code just complains
> >> very loudly that it is broken.
> >> 
> >> Further the code is broken at a design level.  The code isn't
> >> problematic the code is impossible.  The cpu hotplug code can not be
> >> fixed on x86 without a redesign of the generic cpu hotplug code.
> >> 
> >> Suspend does not need to use cpu hotplug because it already gets in
> >> deep with the drivers, and can stop interrupts at the source.  I know
> >> there was some talk about this doing this earlier, but I don't know if
> >> anything came of that discussion.
> >> 
> >> Regardless if you care about this being a problem feel free to fix the
> >> relevant code so it attempts to do something that the hardware
> >> actually supports.
> >> 
> >> But if the suspend needs this code for smp support it is also broken.
> >
> > Well, from the functionality point of view, it's not.  We have no problems
> > with it, at least not that I know of.
> 
> Luck, or enough other issues someone hasn't tracked their problems
> down to this.  On the pure cpu hotplug path I just got a bug
> report about it not working:  http://lkml.org/lkml/2007/5/31/419

[Apart from what I said in the other message:]

In the hibernation/suspend code paths we call the CPU hotplug quite late,
actually right before we turn off local IRQs on the only CPU that is not
offlined.  I think that at this point the majority of interrupt sources should
have been turned off already.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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