Kernel-3.10.0-957.el7_switching-sche

To choose IO schedulers at boot time, use the argument ‘elevator=deadline’.
‘noop’ and ‘cfq’ (the default) are also available. IO schedulers are assigned
globally at boot time only presently.

Each io queue has a set of io scheduler tunables associated with it. These
tunables control how the io scheduler works. You can find these entries
in:

/sys/block//queue/iosched

assuming that you have sysfs mounted on /sys. If you don’t have sysfs mounted,
you can do so by typing:

mount none /sys -t sysfs

As of the Linux 2.6.10 kernel, it is now possible to change the
IO scheduler for a given block device on the fly (thus making it possible,
for instance, to set the CFQ scheduler for the system default, but
set a specific device to use the deadline or noop schedulers - which
can improve that device’s throughput).

To set a specific scheduler, simply do this:

echo SCHEDNAME > /sys/block/DEV/queue/scheduler

where SCHEDNAME is the name of a defined IO scheduler, and DEV is the
device name (hda, hdb, sga, or whatever you happen to have).

The list of defined schedulers can be found by simply doing
a “cat /sys/block/DEV/queue/scheduler” - the list of valid names
will be displayed, with the currently selected scheduler in brackets:

cat /sys/block/hda/queue/scheduler

noop deadline [cfq]

echo deadline > /sys/block/hda/queue/scheduler

cat /sys/block/hda/queue/scheduler

noop [deadline] cfq