2007-10-15 19:22:26 +08:00
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To choose IO schedulers at boot time, use the argument 'elevator=deadline'.
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'noop', 'as' and 'cfq' (the default) are also available. IO schedulers are
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assigned globally at boot time only presently.
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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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2006-04-19 15:23:09 +08:00
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As of the Linux 2.6.10 kernel, it is now possible to change the
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IO scheduler for a given block device on the fly (thus making it possible,
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for instance, to set the CFQ scheduler for the system default, but
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set a specific device to use the anticipatory or noop schedulers - which
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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/hda/queue/scheduler
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noop anticipatory deadline [cfq]
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# echo anticipatory > /sys/block/hda/queue/scheduler
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# cat /sys/block/hda/queue/scheduler
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noop [anticipatory] deadline cfq
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