Re: [PATCH block/for-5.2-fixes] bfq: use io.weight interface file instead of io.bfq.weight

Il giorno 12 giu 2019, alle ore 15:39, Tejun Heo [off-list ref] ha scritto:

On Wed, Jun 12, 2019 at 09:32:07AM +0200, Paolo Valente wrote:

quoted

Could you elaborate a little more on this?

Doesn't seem like you did.

quoted

bfq code for setting up and handling io.weight (more precisely
io.bfq.weight) is a copy and paste of cfq code.

Please take a look at the documentations under
Documentation/cgroup-v1/blk-iocontroller.txt and
Documentation/admin-guide/cgroup-v2.rst.

I'm sorry, but I don't see what doesn't match between BFQ's and CFQ's
implementations of the weight parameter.

So, if you agree, let me paste the two snippets for v1 that involve
weights.  So maybe you can at least tell me 'here' (then I'll try the
same with v2).

----------------------------------------------------------------------

	mount -t tmpfs cgroup_root /sys/fs/cgroup
	mkdir /sys/fs/cgroup/blkio
	mount -t cgroup -o blkio none /sys/fs/cgroup/blkio

- Create two cgroups
	mkdir -p /sys/fs/cgroup/blkio/test1/ /sys/fs/cgroup/blkio/test2

- Set weights of group test1 and test2
	echo 1000 > /sys/fs/cgroup/blkio/test1/blkio.weight
	echo 500 > /sys/fs/cgroup/blkio/test2/blkio.weight

-> This is exactly how you set weights with BFQ

----------------------------------------------------------------------

Details of cgroup files
=======================
Proportional weight policy files
--------------------------------
- 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.

-> This is the exact implementation of the weight parameter in BFQ

BFQ does not implement weight_device, but we are not talking about
weight_device here.  More precisely, *nothing* implements weight_device
any longer in cgroups-v1, so the documentation is wrong altogether.

Looking forward to your feedback,
Paolo

Thanks.

--
tejun