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Switching Scheduler
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===================
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Each io queue has a set of io scheduler tunables associated with it. These
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tunables control how the io scheduler works. You can find these entries
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in::
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/sys/block/<device>/queue/iosched
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assuming that you have sysfs mounted on /sys. If you don't have sysfs mounted,
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you can do so by typing::
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# mount none /sys -t sysfs
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It is possible to change the IO scheduler for a given block device on
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the fly to select one of mq-deadline, none, bfq, or kyber schedulers -
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which can improve that device's throughput.
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To set a specific scheduler, simply do this::
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echo SCHEDNAME > /sys/block/DEV/queue/scheduler
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where SCHEDNAME is the name of a defined IO scheduler, and DEV is the
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device name (hda, hdb, sga, or whatever you happen to have).
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The list of defined schedulers can be found by simply doing
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a "cat /sys/block/DEV/queue/scheduler" - the list of valid names
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will be displayed, with the currently selected scheduler in brackets::
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# cat /sys/block/sda/queue/scheduler
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[mq-deadline] kyber bfq none
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# echo none >/sys/block/sda/queue/scheduler
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# cat /sys/block/sda/queue/scheduler
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[none] mq-deadline kyber bfq
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