Comment # 9 on bug 1178797 from Jan Kara

elevator= parameter stopped working with transition to blk-mq block layer
framework in the kernel (around 5.0 timeframe, not sure exactly, I can find the
commit if you're interested). I created jsc#SLE-10853 for updating the docs and
release notes, the docs were updated, the release note is still WIP with the
docs team :-|.

Anyway for the sake of this bug SLE15-SP2 and anything newer doesn't really
support elevator= kernel argument. Note that there was a relatively long time
frame (between 5.0 and 5.5) when the argument was just silently ignored before
we re-added handler for that argument to at least warn users. And we backported
this warning to our SLE15-SP2 kernels.

WRT other ways of setting the IO scheduler we currently carry udev rules that
setup the elevator for each device as appropriate. That is effectively using
sysfs and is currently the only way how you can influence which IO scheduler is
going to be used for which device.

From installer POV the only way I see how it could influence what elevator the
installed system is going to use (which is what this yast2 feature is about
AFAIU) is that it would modify / add further udev rules tuning the IO scheduler
when the system is booting. Or we could change our udev rules to take into
account some environment variable or something like that (might be useful for
simple setups with single disk).

So probably let's start by thinking what feature / experience do we want to
provide from the installer POV wrt IO scheduler config (I can imagine anything
starting with "nothing" and ending with tool allowing configuring complex set
of rules determining IO scheduler for each device - something like nice
user-friendly dialogues for configuring udev rules)... I'm adding to CC Andreas
Herrmann who was writing the current set of udev rules.