Odd IDE performance drop 2.4 vs 2.6?

[Grant Coady <grant_lkml@dodo.com.au>]

Hi there,

A new 'old' box, with near 3:1 hdparm -Tt /dev/hda performance drop 
comparing 2.4.31 with 2.6.11.12. pII/266 on 440LX chipset. HDD set 
to udma2 (max for h/w) with manuf. utility.  Single master on ribbon.
CDROM on other ribbon.  Two runs each via ssh login soon after boot:

Linux 2.4.31-si.
root@silly:~# hdparm -tT /dev/hda

/dev/hda:
 Timing cached reads:   344 MB in  1.99 seconds = 172.86 MB/sec
 Timing buffered disk reads:   68 MB in  3.02 seconds =  22.52 MB/sec
root@silly:~# hdparm -tT /dev/hda

/dev/hda:
 Timing cached reads:   356 MB in  2.00 seconds = 178.00 MB/sec
 Timing buffered disk reads:   68 MB in  3.04 seconds =  22.37 MB/sec
root@silly:~#

Linux 2.6.11.12a.
root@silly:~# hdparm -tT /dev/hda

/dev/hda:
 Timing cached reads:   340 MB in  2.01 seconds = 168.76 MB/sec
 Timing buffered disk reads:   26 MB in  3.02 seconds =   8.60 MB/sec
root@silly:~# hdparm -tT /dev/hda

/dev/hda:
 Timing cached reads:   340 MB in  2.01 seconds = 169.26 MB/sec
 Timing buffered disk reads:   26 MB in  3.02 seconds =   8.61 MB/sec
root@silly:~#

Hardware info, configs, etc at http://scatter.mine.nu/test/boxen/silly/
--Grant.