| =================== |
| Switching Scheduler |
| =================== |
| |
| 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/<device>/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 |
| |
| It is possible to change the IO scheduler for a given block device on |
| the fly to select one of mq-deadline, none, bfq, or kyber 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/sda/queue/scheduler |
| [mq-deadline] kyber bfq none |
| # echo none >/sys/block/sda/queue/scheduler |
| # cat /sys/block/sda/queue/scheduler |
| [none] mq-deadline kyber bfq |
