linux/Documentation/block/switching-sched.rst
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   1===================
   2Switching Scheduler
   3===================
   4
   5Each io queue has a set of io scheduler tunables associated with it. These
   6tunables control how the io scheduler works. You can find these entries
   7in::
   8
   9        /sys/block/<device>/queue/iosched
  10
  11assuming that you have sysfs mounted on /sys. If you don't have sysfs mounted,
  12you can do so by typing::
  13
  14        # mount none /sys -t sysfs
  15
  16It is possible to change the IO scheduler for a given block device on
  17the fly to select one of mq-deadline, none, bfq, or kyber schedulers -
  18which can improve that device's throughput.
  19
  20To set a specific scheduler, simply do this::
  21
  22        echo SCHEDNAME > /sys/block/DEV/queue/scheduler
  23
  24where SCHEDNAME is the name of a defined IO scheduler, and DEV is the
  25device name (hda, hdb, sga, or whatever you happen to have).
  26
  27The list of defined schedulers can be found by simply doing
  28a "cat /sys/block/DEV/queue/scheduler" - the list of valid names
  29will be displayed, with the currently selected scheduler in brackets::
  30
  31  # cat /sys/block/sda/queue/scheduler
  32  [mq-deadline] kyber bfq none
  33  # echo none >/sys/block/sda/queue/scheduler
  34  # cat /sys/block/sda/queue/scheduler
  35  [none] mq-deadline kyber bfq
  36