linux-kernel - Re: [PATCH 1/5] resources: add arch hook for preventing allocation in reserved areas

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Date:	Mon, 13 Dec 2010 14:47:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Adam Belay <abelay@....edu>, Matthew Garrett <mjg@...hat.com>,
	Dan Williams <dcbw@...hat.com>
Subject: Re: [PATCH 1/5] resources: add arch hook for preventing allocation
 in reserved areas


* Bjorn Helgaas <bjorn.helgaas@...com> wrote:

> > OK, so I guess the best thing we can do for 2.6.37 is to revert 1af3c2e (x86: 
> > allocate space within a region top-down), right?
> 
> That's a possibility, but I'm not sure it's the best.  It would avoid the nx6325 
> landmine, but we could easily step on a different one on other machines.
> 
> If Windows uses the end of available space first, that's the best-tested 
> territory, and I think it's better to try to stay in it rather revert 1af3c2e and 
> start mapping different territory that really isn't tested by Windows at all.
> 
> On the nx6325, we stray out of that tested territory because Linux opens windows 
> on subtractive-decode bridges and allocates more space to CardBus bridges.
> 
> I think it'd be fairly simple to leave subtractive-decode bridges alone, and that 
> might make the nx6325 work well enough for .37, even without the quirk.  This 
> feels like a change that might be the right thing to do in general.  Using 
> subtractive rather than positive decode would give up a little performance, but I 
> doubt it's important

Is there a patch for that that people could try?

The regression needs to be addressed one way or another: either by improving the 
"compatible with Windows" approach to actually work (without quirks), or by 
reverting to the tested-for-years Linux solution.

( What we always try to avoid is trading in a set of regressions for another set of 
  regressions. That way lies madness, it can not result in reliable, provable 
  progress. )

Thanks,

	Ingo
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