Selecting and Tuning a Scheduler
May 11, 2009, 23:33 (1 Talkback[s])
(Other stories by Paul Rubens)
"The obvious first question that must be answered is this: Which
scheduler should you use? It's a deceptively difficult question,
and the answer will depend on many inter-related factors, including
the applications running, the size of the files you are read and
writing, the frequency of your file read and writes, and the
pattern of these reads and writes. The only thing that can be said
with much certainty is that unless you are using a solid state
drive or RAM disk — which can access all files equally fast
— the noop scheduler is the worst choice. The other, active
schedulers should all perform better than noop with conventional
spinning disks.
"There's some evidence that when many different types of
applications are requesting many different types of disk reads and
writes the deadline scheduler is the best all-round performer, but
in the end the best course of action is probably to test all three
active schedulers and choose the one that gives the best
results.
"So once you've chosen a scheduler to test, how do you get your
system to use it? There two primary ways to do this: at boot
through a configuration file or on the fly from the command line.
The examples we use here work for Red Hat Enterprise Linux but
should be similar for any distribution you happen to be using."
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