Re: QoS for iSCSI target?

[Chris Friesen <chris.friesen@windriver.com>]

On 04/02/2016 07:15 PM, Nicholas A. Bellinger wrote:
> On Fri, 2016-04-01 at 12:35 -0600, Chris Friesen wrote:

>>>> On a slightly different note, is there any way to throttle or limit the overall
>>>> bandwidth consumed by the iSCSI target in the kernel?  I'd like to ensure that
>>>> the iSCSI traffic doesn't completely swamp the host accesses to the same block
>>>> device.
>>>>
>>>> I suppose I could do networking-based traffic shaping, but are there any
>>>> controls in the block IO subsystem?
>>>>
>>>
>>> On a individual block_device backend basis, block cgroups is the
>>> preferred method for doing this.
>>>
>>> Note that any rate limiting imposed by block cgroups is subject to the
>>> current se_node_acl->queue_depth enforced across all LUNs within a given
>>> iscsi session.
>>
>>
>> How would I use cgroups with the kernel iSCSI target?  Is there a set of kernel
>> threads dedicated to the iSCSI target that I can assign to a particular group?
>>
>
> block cgroups can set I/O throttling (bandwidth + IOPs) limits for any
> normal struct block_device.
>
> These values are configured via blkio.throttle.* resource class, and the
> limits are imposed independently of the block_device's association with
> target_core_mod backend driver export.  Namely:
>
>      blkio.throttle.write_iops_device
>      blkio.throttle.read_iops_device
>      blkio.throttle.write_bps_device
>      blkio.throttle.read_bdp_device
>
> Some examples using these values, plus more blkio.* info is here:
> http://events.linuxfoundation.org/sites/events/files/slides/cgroups_0.pdf.
>

I understand how to set up the cgroups, but don't I need to ensure that the IO 
operations happen in the context of a particular cgroup?  If so, how do I ensure 
that the in-kernel iSCSI target traffic happens in the context of the specified 
group?  Are there a set of kernel threads dedicated to processing iSCSI requests?

Chris