Message-ID: <SNT125-W530B92A00FA8AFB846085EC33C0@phx.gbl>
From: Yuhong Bao <yuhongbao_386@hotmail.com>
To: <hpa@zytor.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>, <mingo@redhat.com>,
       <linux-kernel@vger.kernel.org>
Subject: RE: Ubuntu 32-bit, 32-bit PAE, 64-bit Kernel Benchmarks
Date: Sun, 28 Feb 2010 17:31:39 -0800
Importance: Normal
In-Reply-To: <4B511B12.6010208@zytor.com>
References: <SNT125-W41CEF6892DBE0B1FD99B4AC3780@phx.gbl>,<4B511B12.6010208@zytor.com>
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>> 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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