linux-kernel - Re: Ubuntu 32-bit, 32-bit PAE, 64-bit Kernel Benchmarks

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Message-ID: <4B3C5F22.1080108@panasas.com>
Date:	Thu, 31 Dec 2009 10:21:54 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Bill Davidsen <davidsen@....com>
CC:	Linux Kernel mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Ubuntu 32-bit, 32-bit PAE, 64-bit Kernel Benchmarks

On 12/31/2009 04:49 AM, Bill Davidsen wrote:
> Yuhong Bao wrote:
>> 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
>>
> I find these tests mirror my own experience with PAE, the benefit of having the 
> nx hardware enabled justifies the few percent drop in performance I was able to 
> find.
> 
> I find the huge gain in web service hard to believe without a hint why a 64 bit 
> CPU would be 15x faster. The disk, memory, and network wouldn't be faster, and 
> the CPU intensive tests weren't significantly faster, so unless the systems were 
> tuned differently where's the gain? Same feeling about the TP test, an order of 
> magnitude faster on a test running the same application on the same hardware is 
> hard to buy without an explanation.
> 

Why? simple, Memory. This system must have lots of memory (see the HIGHMEM64G) so
lots of IO must be bouncing on a 32bit system, where in 64bit it is copy-less.

Just my guess, but I'm not surprised.

> The only obvious source I can think of is running the test load at 100Mbit on
> one test and Gbit on another, because I saw an early network driver do just that
> in negotiations with a switch.
> 

Boaz
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