Balbir Singh wrote:
Peter Williams wrote:
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.
The resource we are controlling is CPU bandwidth,
Unfortunately, most tasks' bursts of CPU are much shorter than the sizes
of the time slices you're allocating (and the faster CPUs get the more
this will be the case) so they don't have much effect.
what other parameters
can we
use to control it?
Dynamic priority.
. Nice values indirectly control the time a task gets,
but
also affects its priority. Even if a task is not CPU bound, we are only
interested in its CPU bandwidth utilization in the CPU resource controller.
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.
The problem with controlling nice values that I see is that nice values
do not
necessarily linearly map CPU time. Changing the nice value also changes the
priority, which impacts the order in which tasks are run.
It's my belief that time and priorities are orthogonal. Nice does a good
job
of trying to mix the two, but in the case of resource management it
might not
be such a good idea.
Think "dynamic priorities".
Peter
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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