SRU IO Scheduler in Kubuntu 14.04

[Harald Sitter]

alohas dearest technical board members,

I would like to kindly request the TBs input on a possible IO
scheduler changing SRU for Kubuntu 14.04.

The gist of it is: all of ubuntu is using deadline scheduler, KDE's
file indexer needs to set ioniceness to not hijack the computer on
systems with HDDs, so Kubuntu needs to set the CFQ scheduler (which
supports ioniceness) in such scenarios. We'd like to SRU a fix for
this in 14.04 and are looking for input on the matter.

CFQ is being set by the kubuntu-settings package in kubuntu
installations starting with 14.10. [0]

Unfortunately we and upstream did not notice that a lot of the speed
problems WRT indexing in Kubuntu 14.04 came in fact from deadline
being not very suitable for the way indexing is done (on HDDs, has to
do with how deadline works also see [1] for a discussion on the
matter). So we released with deadline (as per ubuntu default).
Since then this has caused numerous bug reports, flame wars on various
social media sites, complaints in forums general hostility towards
upstream and the kubuntu team, and a lot of time wasted on rehashing
why 14.04 is not delivering the quality that we and upstream intended.

It is due to all of this that we are looking into landing an SRU [2]
for 14.04 also forcing Kubuntu installations with HDDs to use the CFQ
scheduler instead of deadline. SSD installations would not be affected
and continue to use deadline.

As seen in comment #5 of [2] it was suggested to wait until after the
release of 14.10 and only then proceed with the SRU. Most Kubuntu devs
do not appear to agree with this as being too conservative an
approach. The possible fallout is highly limited in impact (could only
make some things slower) and scope (only could do so on Kubuntu with
HDD).

I think Jonathan Riddell's comment sums it up pretty well:
"we know upstream linux recommends it, we know baloo [kde indexer]
recommends it, ubuntu kernel team don't seem too sure why they
switched, we don't have any reason to think it'll
cause problems"

Would the technical board support a swifter resolution of the problem
or indeed prefer waiting?

TIA
HS

[0] http://goo.gl/9XFijy
[1] http://irclogs.ubuntu.com/2014/10/08/%23ubuntu-kernel.html#t12:56
[2] https://bugs.launchpad.net/bugs/1378789