Today, I discovered a gem added to the 2.6.9 Linux kernel by Intel engineer Venkatesh Pallipadi: the Ondemand cpufreq governor. This kernel module uses the Enhanced SpeedStep Technology available with Pentium M processors to rapidly change the CPU speed, based on current load.

cpuspeed does the same thing, but takes noticeably longer to reach the maximum speed, and also waits longer before slowing down again. X applications feel much faster with Ondemand, and my guess is that battery life will be slightly better.

So if you have an Intel CPU with Enhanced SpeedStep Technology and want to give Ondemand a try, stop any running cpufreq daemons, like cpuspeed or cpudyn, and run the following commands. Note that I have only tested this on Fedora Core 3 with the 2.6.11-1.14_FC3 kernel.

/sbin/modprobe cpufreq_ondemand
echo ondemand > /sys/devices/system/cpu/*/cpufreq/scaling_governor

You can then start

watch -n 1 cat /sys/devices/system/cpu/*/cpufreq/scaling_cur_freq

in a terminal window, and run some X application to see how Ondemand changes the CPU speed.

To permanently install Ondemand, make sure that the cpuspeed service is turned off, and add the above modprobe and echo commands to /etc/rc.d/rc.local.

If you want to switch back to cpuspeed for some reason, you can deactivate Ondemand by running

echo userspace > /sys/devices/system/cpu/*/cpufreq/scaling_governor

Ever got I/O errors on CDs burned with cdrecord under Linux, although you were 100% sure the ISO image and the CD medium was OK?

I had that experience yesterday, while on-site at a customer. The I/O errors always occurred at the end of the burned CD, when I ran md5sum /dev/cdrom.

Today, I found this in the cdrecord manual:

-raw96r: This is the preferred raw writing mode as it gives best control over the CD writing process. [...] There are several CD writers with bad firmware that result in broken disks when writing in TAO or SAO mode.

I guess the Samsung CDRW/DVD SN-324S, revision U303, which came with my Dell Latitude D800, is one of them. Running cdrecord with the -raw96r option results in perfectly readable CDs with correct MD5 digests.

Interestingly enough, we had the same problem on the customer's IBM notebook running Nero under MS Windows.