slow dvd-ram write since kernel 2.6.8
 

Hi,

DVD-RAM writing is much slower than to be expected on my system since I upgraded to kernels newer than 2.6.7.

I have a LG GSA-4163B burner (also tested a 4120, same problem) which can write DVD-RAM at 3x, which makes 1.5x including automatic verify - about 1.9MB/s.

This is exactly what I get with a vanilla 2.6.7.

I then tried vanilla 2.6.8, 2.6.9, 2.6.10 and stock ubuntu 2.6.8.1, 2.6.9 and 2.6.10.
With all of those, writing is considerably slower: about 800 kB/s to 1 MB/s. The drive's head seems to be jumping much more than with 2.6.7.

I tried udf and ext2 filesystems (2048k block size), I checked the settings of the io-scheduler (seem to be identical).

No errors in dmesg while writing.


All tests were made with some command like
(well, that's huge, but values were still 25% too high with just 1G: nearly 2.5MB/s with 2.6.7, which is impossible)

I also tested writing directly to the device with dd, this seemed to be a bit faster.


The device is connected either via onboard ide (dma is on, of course) or with an external usb2 case whith which I got about 25MB/s r/w when I tested it with a HD drive.

I do not understand the changes made in the 2.6.8 kernel, and I do not even really know where to seach.

Hardware info:
ASUS K8V SE Deluxe board, AMD64 Newcastle 3000+, (what else could be useful?)


Any ideas?

No Ides anyone?

Is seems to be broken since 2.6.7-bk8, as I now found out. But still, there are many changes between bk7 and bk8, none of which I understand (I am not a programmer, unfortunately).