[SRU] Set the default IO scheduler to CFQ in Kubuntu Trusty

Wed Oct 8 16:42:48 UTC 2014

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On 08/10/14 17:36, Steve Langasek wrote:
> Hi Jonathan,
> 
> On Wed, Oct 08, 2014 at 03:56:42PM +0100, Jonathan Riddell wrote:
>> Me and Rohan would like a second opinion on bug 1378789
>>  [SRU] Set the default IO scheduler to CFQ in Kubuntu Trusty
>>  https://launchpad.net/bugs/1378789
> 
>> The kernel team have changed the scheduler away from upstream Linux
>> defaults to deadlock which causes our desktop indexing programme Baloo
>> to run very slow and take up lots of resources because it doesn't
>> implement ionice suport.  We'd like to update kubuntu-settings with a
>> udev rule to change back to CFQ.
> 
>> We've changed this in utopic.  There's minimal chance of regressions,
>> it's an upstream default recommended by Linux and Baloo.  We're
>> getting quite a few reports of people saying their system is sluggish
>> and the baloo upstream author is most grumpy.
> 
>> Scott would rather wait until after utopic is out where it would get
>> more testing, but I doubt there will be much that most users can say
>> beyond "it's not horribly slow".
> 
> I don't think it's at all appropriate for a desktop environment to install a
> udev rule which changes the kernel scheduler.  That's a severe layering
> violation, and it means that anyone who installs kubuntu-desktop on an
> existing system will significantly change the performance characteristics of
> that system.
> 
> I also think it's categorically wrong to say that there's minimal chance of
> regression.  These schedulers have pretty fundamentally different
> characteristics, and where CFQ behaves pathologically for one process (the
> indexer), deadline will behave pathologically for others.
> 
> I don't think it's at all acceptable to work around a kernel bug in a
> kubuntu-settings SRU.  The right fix is to resolve this in the kernel
> package instead. (Bug #1310402)  Cc:ing the kernel team.
> 
> Also, what exactly do you mean when you say baloo doesn't "implement ionice
> support"?  The 'ionice' tool is part of the base system (util-linux).  It
> would be a simple matter of packaging to always run baloo under ionice.

Linux supports I/O scheduling priorities since 2.6.13 just with the CFQ
io scheduler.