IO slowdown with latest FC4 kernel

[Dave Jones]

On Fri, Sep 30, 2005 at 11:43:51PM -0300, Pedro Fernandes Macedo wrote:
 > Hello guys. I think I've stumbled across something weird.
 > My brother updated his machine today and since then he started to have 
 > horrible IO performance with kernel-2.6.13-1.1526_FC4. For example, 
 > transfering his stuff to my computer as a backup (we started to suspect 
 > the HDDs were going to stop working), the max speed with latest kernel 
 > was below 1MB/s. With  2.6.12-1.1456_FC4, transfer speed is over 3MB/s 
 > according to the ssh client I'm using right now.
 > Not to mention the average responsiveness of the system (a ssh login 
 > with 1526 took about 10-20 seconds to show the login prompt, while with 
 > 1456 the prompt shows up immediately.
 > 
 > Any ideas on how I can test this to confirm if this is a bug or just 
 > faulty hardware? I'm going to run a full smart test on the discs 
 > tomorrow and a few RAM checks just in case, but the short test from 
 > smart passed without any problems and the smart reports shows no 
 > parameter outside the limits.

What kind of disk controller ? If IDE, is DMA enabled ?
 
It would be interesting to see the output of ..

<boot old kernel>
dmesg -s 128000 >dmesg.old
<boot new kernel>
dmesg -s 128000 >dmesg.new
diff -u dmesg.old dmesg.new

		Dave