On 04/04/2016 04:29 PM, Nicholas A. Bellinger wrote:
On Mon, 2016-04-04 at 09:20 -0600, Chris Friesen wrote:
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?
block cgroups does I/O ratelimiting at struct block_device level.
Eg: The process cgroup (which AFAICT is what your thinking about) is
separate from block cgroups, and doesn't need to be explicitly enabled
in order for block cgroup to function.
I'm still confused.
I'm not trying to globally throttle IO on a particular block device. I'm trying
to control how much IO the iSCSI target in the kernel is allowed to drive on a
particular block device.
The goal is to ensure that the iSCSI target does not consume all of the
available bandwidth for a particular block device. I want to ensure that some
of the bandwidth for that device is available to other processes on the host
(for management purposes) rather than being consumed by a greedy iSCSI initiator.
In an ideal world I would like a set of rules that say things like:
1) if there is contention, ensure that the host is guaranteed X percent of the
available /dev/sdb IOPS
2) if there is contention, do not allow the iSCSI target traffic to consume more
than Y percent of /dev/sdb's write traffic
Chris
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