linux-kernel - Possible 32-bit PAE kernel I/O slow down with 3.3.X

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Date:	Thu, 26 Apr 2012 21:53:44 -0400
From:	Joe Ceklosky <jfceklosky@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Possible 32-bit PAE kernel I/O slow down with 3.3.X

I have notice significant slow downs with disk I/O on a 32-bit PAE 3.3.X 
kernels.

The test machine has 16GB memory, Intel i5 CPU, Intel
motherboard, and an Intel 160GB SSD.  I copied 536M from one partition 
on an SSD to another.
Yes, I should be using a 64bit kernel with 16GB!

Test 1:
kernel 3.3.2 32-bit PAE with kernel parm mem=3G

time cp -ra testdir/ /tmp
real    0m8.989s
user    0m0.094s
sys     0m1.080s

Test 2:
kernel 3.3.2 32-bit PAE

time cp -ra testdir/ /tmp
real    1m17.068s
user    0m0.173s
sys     0m2.149s

Also I tested kernel 3.2.16 32-bit PAE with no memory limits 16GB and it
was in line with test 1.

I can repeat and provide any debugging information if needed.

Thanks,
Joe Ceklosky
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