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From:   Paolo Valente <paolo.valente@linaro.org>
Message-Id: <262EE1CC-7473-4D4C-B108-734ACED1623C@linaro.org>
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Subject: Re: Setting up default iosched in 5.0+
Date:   Fri, 24 May 2019 17:38:41 +0200
In-Reply-To: <x49ftp329lt.fsf@segfault.boston.devel.redhat.com>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        Jens Axboe <axboe@kernel.dk>, Ming Lei <ming.lei@redhat.com>,
        Omar Sandoval <osandov@fb.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
To:     Jeff Moyer <jmoyer@redhat.com>
References: <20190518093310.GA3123@avx2>
 <x49ftp329lt.fsf@segfault.boston.devel.redhat.com>
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> Il giorno 24 mag 2019, alle ore 16:46, Jeff Moyer <jmoyer@redhat.com> =
ha scritto:
>=20
> Hi, Alexey,
>=20
> Alexey Dobriyan <adobriyan@gmail.com> writes:
>=20
>> 5.0 deleted three io schedulers and more importantly =
CONFIG_DEFAULT_IOSCHED
>> option:
>>=20
>> 	commit f382fb0bcef4c37dc049e9f6963e3baf204d815c
>> 	block: remove legacy IO schedulers
>>=20
>> After figuring out that I silently became "noop" customer enabling =
just
>> BFQ didn't work: "noop" is still being selected by default.
>>=20
>> There is an "elevator=3D" command line option but it does nothing.
>>=20
>> Are users supposed to add stuff to init scripts now?
>=20
> 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.
>=20

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.
>=20
> 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=3D kernel command line parameter:
>=20
> =
https://github.com/lnykryn/systemd-rhel/blob/rhel-8.0.0/rules/40-elevator.=
rules
>=20
> Cheers,
> Jeff


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