linux-kernel - Re: Why such a big difference in init-time PCI resource call-paths (x86 vs x86

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Date:	Thu, 01 May 2008 14:11:50 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
CC:	Andi Kleen <andi@...stfloor.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-pci@...ey.karlin.mff.cuni.cz, TJ <linux@...orld.net>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Why such a big difference in init-time PCI resource call-paths
 (x86 vs x86_64) ?

Yinghai Lu wrote:
> On Thu, May 1, 2008 at 1:11 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> On Thu, May 01, 2008 at 11:16:31AM -0700, Jesse Barnes wrote:
>>  > On Wednesday, April 30, 2008 9:07 am TJ wrote:
>>  > > In preparation for writing a Windows-style PCI resource allocation
>>  > > strategy
>>  > >
>>  > >  - use all e820 gaps for IOMEM resources; top-down allocation -
>>  > >
>>  > > and thus giving devices with large IOMEM requirements more chance of
>>  > > allocation in the 32-bit address space below 4GB (see bugzilla #10461),
>>
>>  I tried that some time ago and it turned out that some systems have
>>  mappings in holes and don't boot anymore when you fill the holes too much.
>>  But that was only considering e820. if you do this it might work if you
>>  do it really like windows and consider all resources, including ACPI.
> 
> wonder if using holes in MTRR AND e820 could help...
> 

Typically not, since the MTRRs won't tell you what is free address space 
and what is occupied by non-BAR I/O devices.

	-hpa
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