[GLLUG] Initialising /sys

Hearns, John john.hearns at mclaren.com
Mon Jul 15 08:34:37 UTC 2013

I am running Centos 6, I wish to tweak something under /sys on boot, what is the
best way of doing it ?

If I want to initialise something under /proc I can put it into /etc/sysctl.conf
--- is there something equivalent for /sys ?

OK: I can always write my own init script, but ....

What I want to achieve is:

    echo 1 > /sys/devices/system/cpu/sched_smt_power_savings

On SuSE  systems you would consider putting this in /etc/init.d/boot.local

which will:

    One core will be filled with tasks before tasks will be moved to other
    cores. The idea is to concentrate the running tasks on a relatively small
    number of cores, allowing the others to remain idle.

Funnily enough, you do exactly the opposite in HPC (high performance computing.
In an optimal situation, your code will run at (you hope) 100% of a core.
So you match the number of processes you run per node with the core count, and use NUMA tools
to place each process on a core.
Actually, it CAN give you performance gains in multi-core processors to run on alternate cores,
Eg. If hyperthreading is enabled or if cores share a cache.

If you're looking at where your processes are running,  htop is a great tool for this:

(top can of course show this information - but htop is like top on steroids)

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