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

[Steve Langasek]

On Tue, Oct 14, 2014 at 07:25:16AM +0200, Harald Sitter wrote:
> On Tue, Oct 14, 2014 at 2:07 AM, Scott Kitterman <ubuntu at kitterman.com> wrote:
> >> Given that essentially lowest priority is requested under CFQ,
> >> equivalent result should be possible to achieve with cgroups
> >> containment.
> >> Specifically by limiting CPU (cpu.shares set to 100 ~= 1/10 of the
> >> default 1024) and/or IO weight (blkio.weight) and bandwidth
> >> (blkio.throttle.read_bps_device / blkio.throttle.write_iops_device) of
> >> the baloo process. This would then be a scheduler-independent solution
> >> and make baloo a truly capped resources background process.

> > Are you offering to implement this?

> Implementation aside, I am not sure this would be a suitable
> replacement (someone should check with upstream ;)). From what I
> gather the notion is that baloo should index as fast as possible given
> resources are available. Throttling through a cgroup containment would
> lower the available resources in general, wouldn't it? This is
> supposedly why ioniceness was used instead. If nothing is going on the
> indexer can work at full speed, while if the user is actually doing
> something baloo essentially allows the kernel to IO starve it to allow
> the rest of the system to be snappy.

  - blkio.weight
	- Specifies per cgroup weight. This is default weight of the group
	  on all the devices until and unless overridden by per device rule.
	  (See blkio.weight_device).
	  Currently allowed range of weights is from 10 to 1000.

  https://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt

However, this file also says:

   Currently two IO control policies are implemented. First one is
   proportional weight time based division of disk policy.  It is
   implemented in CFQ.

So in fact, ths seems to suffer from the same limitation as ionice.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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