Balbir Singh wrote:
On 8/30/06, Martin Ohlin <[email protected]> wrote:
To those interested
I have been working on a CPU resource controller using the nice value as
a control signal. At the moment, the control is done on a
per-task-level, but I have plans to extend it to groups of tasks. The
control is based on a PI-controller (Proportional, Integral), using an
execution time measurement as input to the controller, and the output
from the controller as nice value.
The CKRM e-series is a PID based CPU Controller. It did a good job of
controlling and smoothing out the load (and variations) and even
worked with groups. But it achieved all this through some amount of
complexity. How do you plan to extend the idea to groups? Do you have
any code that we can look at?
I do not understand controlling the nice value? Most cpu control the
bandwidth/time - are there any advantages to controlling the nice
value?
Trying to control CPU allocations purely using time allocations will
only work well for CPU bound processes. Furthermore, the faster CPUs
become the more this will be the case.
How does this interplay with dynamic priorities that the
scheduler currently maintains?
But your implication here is valid. It is better to fiddle with the
dynamic priorities than with nice as this leaves nice for its primary
purpose of enabling the sysadmin to effect the allocation of CPU
resources based on external considerations. Having said that I would
also opine that the basic mechanism this author uses to fiddle the nice
values could be applied to the dynamic priorities instead with the key
difference being that nice can be fiddled from outside the scheduler but
you really need to be inside the scheduler to fiddle with dynamic
priorities.
Using the controller, it is possible to make CPU reservations that in a
soft way guarante that tasks achieve as much resources as the
corresponding reference indicates.
For those interested, the concept is described in more detail along with
experiments in the first part of my thesis available at:
http://www.control.lth.se/database/publications/article.pike?artkey=ohlin06lic
Read one more paper - time
Balbir
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