linux-kernel - Re: Setting up default iosched in 5.0+

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Message-Id: <262EE1CC-7473-4D4C-B108-734ACED1623C@linaro.org>
Date:   Fri, 24 May 2019 17:38:41 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jeff Moyer <jmoyer@...hat.com>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Jens Axboe <axboe@...nel.dk>, Ming Lei <ming.lei@...hat.com>,
        Omar Sandoval <osandov@...com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Setting up default iosched in 5.0+



> Il giorno 24 mag 2019, alle ore 16:46, Jeff Moyer <jmoyer@...hat.com> ha scritto:
> 
> Hi, Alexey,
> 
> Alexey Dobriyan <adobriyan@...il.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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