linux-kernel - Re: [PATCH -v3 14/14] x86, mm: Map ISA area with connected ram range at the same time

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Message-ID: <20120906141305.GA10013@jshin-Toonie>
Date:	Thu, 6 Sep 2012 09:13:14 -0500
From:	Jacob Shin <jacob.shin@....com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Tejun Heo <tj@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v3 14/14] x86, mm: Map ISA area with connected ram range
 at the same time

On Thu, Sep 06, 2012 at 10:22:19AM +0300, Pekka Enberg wrote:
> On Wed, Sep 5, 2012 at 1:02 AM, Pekka Enberg <penberg@...nel.org> wrote:
> > > How significant is the speed gain? The "isa_done" flag makes code flow
> > > more difficult to follow.
> 
> On Wed, 5 Sep 2012, Yinghai Lu wrote:
> > Not really much.
> > 
> > when booting system:
> > memmap=16m$128m memmap=16m$512m memmap=16m$256m memmap=16m$768m memmap=16m$1024m
> > 
> > with the patch
> > [    0.000000] init_memory_mapping: [mem 0x00000000-0x07ffffff]
> > [    0.000000]  [mem 0x00000000-0x07ffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x09000000-0x0fffffff]
> > [    0.000000]  [mem 0x09000000-0x0fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x11000000-0x1fffffff]
> > [    0.000000]  [mem 0x11000000-0x1fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x21000000-0x2fffffff]
> > [    0.000000]  [mem 0x21000000-0x2fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x31000000-0x3fffffff]
> > [    0.000000]  [mem 0x31000000-0x3fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x41000000-0x7fffdfff]
> > [    0.000000]  [mem 0x41000000-0x7fdfffff] page 2M
> > [    0.000000]  [mem 0x7fe00000-0x7fffdfff] page 4k
> > 
> > otherwise will have
> > 
> > [    0.000000] init_memory_mapping: [mem 0x00000000-0x000fffff]
> > [    0.000000]  [mem 0x00000000-0x000fffff] page 4k
> > [    0.000000] init_memory_mapping: [mem 0x00100000-0x07ffffff]
> > [    0.000000]  [mem 0x00100000-0x001fffff] page 4k
> > [    0.000000]  [mem 0x00200000-0x07ffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x09000000-0x0fffffff]
> > [    0.000000]  [mem 0x09000000-0x0fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x11000000-0x1fffffff]
> > [    0.000000]  [mem 0x11000000-0x1fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x21000000-0x2fffffff]
> > [    0.000000]  [mem 0x21000000-0x2fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x31000000-0x3fffffff]
> > [    0.000000]  [mem 0x31000000-0x3fffffff] page 2M
> > [    0.000000] init_memory_mapping: [mem 0x41000000-0x7fffdfff]
> > [    0.000000]  [mem 0x41000000-0x7fdfffff] page 2M
> > [    0.000000]  [mem 0x7fe00000-0x7fffdfff] page 4k
> 
> OK. Is there any other reason than performance to do this?

May be minor, but ..

The first range [mem 0x00000000-0x07ffffff] is covered entirely by 2M
page tables, instead of some 4K + some 2M.

-Jacob

> 
> 			Pekka
> 

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