Physics Hacker

If you need to find out the number of CPUs or CPU cores or cores per CPU of your system, you could look it up in /proc/cpuinfo but it’s quite hard to figure out the right parameters. A good overview on the parameters for different system configurations can be found here. If you want to put the actual numbers in variables, here is a nice way to do it:

export CORES_PER_CPU=`grep -c "physical id.*: 0" /proc/cpuinfo`
export CPU_TOTAL=`grep -c "core id.*: 0" /proc/cpuinfo`
export CORE_TOTAL=`grep -c processor /proc/cpuinfo`

/proc/cpuinfo shows an entry for each CPU core. The physical id is incremented for each physical CPU. If the entry has the same physical id as another core, the core belongs to the same CPU. Therefore counting the number of entries with physical id set to 0 results in the number of cores per CPU. The core id is incremented for each core on a physical CPU. Therefore counting the number of entries with core id set to 0 results in the number of physical CPUs. The total number of cores can be retrieved quite easily by counting the number of processor entries.

Unfortunately the above method does not work on all systems. I noticed on some systems with single core processors, that the values core id and physical id are not present.

I searched for official documentation on the proc filesystem, but only found the following document which doesn’t describe the cpuinfo values:

• http://www.kernel.org/doc/Documentation/filesystems/proc.txt

If someone happens to know a better documentation I would be glad if he/she would share it with me!

Manually creating a password under linux for e.g. /etc/shadow or kickstart isn’t really easy. I searched for a while until I found the userdbpw utility. On Debian Systems (including Ubuntu) it can be installed with

apt-get install courier-authlib-userdb

For most distributions the md5 algorithm is used to create passwords. The userdbpw command for md5 passwords is:

userdbpw -md5

More information on userdbpw can be found in its manpage.

So Summer is getting hot and fans are starting to roar. So if you appreciate some silence in the office and just happen to have a Fujitsu Siemens ESPRIMO with P4 on your desk this is for you.

This works for SLC 4 on Fujitsu Siemens ESPRIMO with P4

Install sysutils:

yum install sysfsutils

load module p4_clockmod:

modprobe p4_clockmod

check available schedulers and frequencies:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies

if needed load “ondemand” scheduler:

modprobe cpufreq_ondemand;

check current frequency and scheduler:

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

make “ondemand” the active scheduler:

echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

make changes permanent:

echo “modprobe p4_clockmod” >> /etc/rc.modules

echo “modprobe cpufreq_ondemand” >> /etc/rc.modules

chomod u+x /etc/rc.modules

echo “devices/system/cpu/cpu0/cpufreq/scaling_governor=ondemand >> /etc/sysfs.conf

I stole some of this from this german Howto on CPU scaling.