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Date:	Sun, 28 Feb 2010 17:31:39 -0800
From:	Yuhong Bao <yuhongbao_386@...mail.com>
To:	<hpa@...or.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>, <mingo@...hat.com>,
	<linux-kernel@...r.kernel.org>
Subject: RE: Ubuntu 32-bit, 32-bit PAE, 64-bit Kernel Benchmarks



>> Given that Linus was once talking about the performance penalties of PAE and HIGHMEM64G, perhaps you'd find these benchmarks done by Phoronix of interest:
>> http://www.phoronix.com/scan.php?page=article&item=ubuntu_32_pae
>>
>
> The big difference isn't between HIGHMEM4G (no PAE) and HIGHMEM64G
> (PAE), it's between HIGHMEM and !HIGHMEM. That cutoff is ~892 MB for a
> stock 32-bit kernel.
BTW, Linus posted this about HIGHMEM and PAE:
http://www.realworldtech.com/forums/index.cfm?action=detail&id=78966&threadid=78766&roomid=2
A few corrections though. HIMEM.SYS was never about memory windowing, EMS was.
The way the 286 could access 16MB of memory was plain old segmentation, just in a different way than EMS did.
And the main issue with PAE in Windows was driver issues, I think, which is why when they enabled PAE to get the NX bit, they limited physical address space to 32-bit on client versions of Windows.

Yuhong Bao
 		 	   		  
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