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SubjectRe: Setting up default iosched in 5.0+
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> Il giorno 24 mag 2019, alle ore 16:46, Jeff Moyer <jmoyer@redhat.com> ha scritto:
>
> Hi, Alexey,
>
> Alexey Dobriyan <adobriyan@gmail.com> writes:
>
>> 5.0 deleted three io schedulers and more importantly CONFIG_DEFAULT_IOSCHED
>> option:
>>
>> commit f382fb0bcef4c37dc049e9f6963e3baf204d815c
>> block: remove legacy IO schedulers
>>
>> After figuring out that I silently became "noop" customer enabling just
>> BFQ didn't work: "noop" is still being selected by default.
>>
>> There is an "elevator=" command line option but it does nothing.
>>
>> Are users supposed to add stuff to init scripts now?
>
> A global parameter was never a good idea, because systems often have
> different types of storage installed which benefit from different I/O
> schedulers. The goal is for the default to just work.
>

Just for completeness, the current default is the worst possible
choice on all systems with a speed below 500 KIOPS, which includes
practically all personal systems ;) But this is a different story ...

Thanks,
Paolo

> If you feel that the defaults don't work for you, then udev rules are
> the way to go.
>
> If you also feel that you really do want to set the default for all
> devices, then you can use the following udev rule to emulate the old
> elevator= kernel command line parameter:
>
> https://github.com/lnykryn/systemd-rhel/blob/rhel-8.0.0/rules/40-elevator.rules
>
> Cheers,
> Jeff

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