Comment 82 for bug 131094

I have tried the vanilla kernel (2.6.22-14) on Gutsy. Now I get better disc performance, (ext3 / bs=10 ~4MB/s / bs=100 7MB/s), but desktop responsiveness becomes worse.
I have tried Hardy too for a while and recognise, that the responsiveness of the desktop is sometimes worse than under gutsy, even when there is no or light disc access only.
Sometimes the gnome menu needs about 2 seconds before it appears. And there are only logos and metadata to load. This are the problems as in gutsy and especially in gusty with 2.6.22 kernel.
Hdparm reposts, that UDMA is on. And there is only iowait cpu consume on lowest cpu frequency and a great disc performace, when coping a normal blocksize (>= 4k) with dd.
Compiz is disabled on every of my installation. I use a 64-bit version of gutsy and hardy.
I don't know the internal design of the linux kernel, so it's only a guess of mine. There must be a bottleneck, which is especially caused by high disc access, but also occurs on other activities. Perhaps interrupt handling. Powertop reports ~400 awaking of the keyboard while copying to files from one partition to another partition with a block size of 4k and writing this text. And I am writing only maximal two or three letters per second. And the count is only as high, when coping the files. Without disc access there are only about 200 awaking, while writing in the same speed.

With two writing and two reading disc access
  38,9% (445,7) <interrupt> : PS/2 keyboard/mouse/touchpad
  17,5% (200,7) <interrupt> : extra timer interrupt
  14,5% (165,8) <interrupt> : libata
   8,8% (100,5) <interrupt> : uhci_hcd:usb1, eth0

Without high io access
  31,2% (213,6) <interrupt> : extra timer interrupt
  25,6% (175,2) <interrupt> : PS/2 keyboard/mouse/touchpad
  14,7% (100,5) <interrupt> : uhci_hcd:usb1, eth0
   8,9% ( 60,8) <interrupt> : uhci_hcd:usb3, ahci, yenta, nvidia