I Have a Schedule to Keep – IO Schedulers

“The schedulers do exactly what the title says — they
schedules activities within the kernel. Since this column is all
about IO, the scheduler of interest is, aptly enough, the IO
scheduler. This article discusses the IO scheduler concepts and the
various options that are available.

“Introduction – IO Scheduler Concepts

“Virtually all applications running on Linux do some sort of IO.
Even surfing the web produces a great number of small files that
are written to disk. Without an IO scheduler, every time there is
an IO request, there is an interrupt to the kernel and the IO
operation is performed. More over, you can get a great mix of IO
operations that move the disk head around the disk to satisfy read
and write operations to different blocks on the drives. Perhaps
more importantly, over time the disparity in the performance of
disk drives and the rest of the system has grown very rapidly
meaning that IO has become more important to overall system
performance. As you can imagine when the kernel has to address the
interrupt so any kind of processing or interactive work is paused.
Consequently the system may appear unresponsive, or it may appear
that the system has slowed down.”

Complete
Story