Date:	Thu, 22 Aug 2013 09:52:09 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Zhang Yanfei <zhangyanfei.yes@...il.com>,
	Tang Chen <tangchen@...fujitsu.com>, konrad.wilk@...cle.com,
	robert.moore@...el.com, lv.zheng@...el.com, rjw@...k.pl,
	lenb@...nel.org, tglx@...utronix.de, mingo@...e.hu, hpa@...or.com,
	akpm@...ux-foundation.org, trenn@...e.de, yinghai@...nel.org,
	jiang.liu@...wei.com, wency@...fujitsu.com, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	mgorman@...e.de, minchan@...nel.org, mina86@...a86.com,
	gong.chen@...ux.intel.com, vasilis.liaskovitis@...fitbricks.com,
	lwoodman@...hat.com, riel@...hat.com, jweiner@...hat.com,
	prarit@...hat.com, zhangyanfei@...fujitsu.com,
	yanghy@...fujitsu.com, x86@...nel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 0/8] x86, acpi: Move acpi_initrd_override() earlier.

Hello Tejun,

On Wed, 2013-08-21 at 23:32 -0400, Tejun Heo wrote:
> On Wed, Aug 21, 2013 at 04:36:35PM -0600, Toshi Kani wrote:
> > I agree that ACPI is rather complicated stuff.  But in my experience,
> > the majority complication comes from ACPI namespace and methods, not
> > from ACPI tables.  Do you really think ACPI table init is that risky?  I
> > consider ACPI tables are part of the minimum config info, esp. for
> > legacy-free platforms.
> 
> It's just that we're talking about the very first stage of boot.  We
> really don't do much there and pulling in ACPI code into that stage is
> a lot by comparison.  If that's gonna happen, it needs pretty strong
> justification.

It moves up the ACPI table init code, which itself is simple.  And ACPI
tables are defined to be pursed at early boot-time, which is why they
exist in addition to ACPI namespace/methods.  They are similar to EFI
memory table.  Firmware publishes tables in one way or the other.

I understand that you are concerned about stability of the ACPI stuff,
which I think is a valid point, but most of (if not all) of the
ACPI-related issues come from ACPI namespace/methods, which is a very
different thing.  Please do not mix up those two.  The ACPI
namespace/methods stuff remains the same and continues to be initialized
at very late in the boot sequence.

What's making the patchset complicated is acpi_initrd_override(), which
is intended for developers and allows overwriting ACPI bits at their own
risk.  This feature won't be used by regular users. 

> > earlyprintk is just another example to this SRAT issue.  The local page
> > table is yet another example.  My hope here is for us to be able to
> > utilize ACPI tables properly without hitting this kind of ordering
> > issues again and again, which requires considerable time & effort to
> > address.
> 
> So, the two things brought up at this point are early parsing of SRAT,
> which can't really solve the problem at hand anyway, 

If you are referring the issue of kernel image location, it is a
limitation in the current implementation, not a technical limitation.  I
know other OS that supports movable memory and puts the kernel image
into a movable memory with SRAT by changing the bootloader.

Also, how do you support local page tables without pursing SRAT early?

> and earlyprintk
> which should be implemented in minimal way which is not activated
> unless specifically enabled with earlyprintk boot param.  Neither
> seems to justify pulling in full ACPI into early boot, right?

Initializing page tables on large systems may take a long time, and I do
think that earlyprink needs to be available before that point.

Thanks,
-Toshi

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