On Thu, Feb 25 2016 at 2:48am -0500, Nikolay Borisov <kernel@xxxxxxxx> wrote: > > > On 02/24/2016 08:12 PM, Chris Friesen wrote: > > > > Hi, > > > > Are there known limitations with the blkio cgroup controller when used > > with LVM? > > > > I'm using Ubuntu 15.10 with the 4.2 kernel. I got the same results with > > CentOS 7. > > > > I set up two groups, /sys/fs/cgroup/blkio/test1 and > > /sys/fs/cgroup/blkio/test2. I set the weight for test1 to 500, and the > > weight for test2 to 1000. > > The weighed mode of blkio works only with CFQ scheduler. And as far as I > have seen you cannot set CFQ to be the scheduler of DM devices. In this > case you can use the BLK io throttling mechanism. That's what I've > encountered in my practice. Though I'd be happy to be proven wrong by > someone. I believe the following sentence in the blkio controller states > that: > " > First one is proportional weight time based division of disk policy. It > is implemented in CFQ. Hence this policy takes effect only on leaf nodes > when CFQ is being used. > " Right, LVM created devices are bio-based DM devices in the kernel. bio-based block devices do _not_ have an IO scheduler. Their underlying request-based device does. I'm not well-versed on the top-level cgroup interface and how it maps to associated resources that are established in the kernel. But it could be that the configuration of blkio cgroup against a bio-based LVM device needs to be passed through to the underlying request-based device (e.g. /dev/sda4 in Chris's case)? I'm also wondering whether the latest cgroup work that Tejun has just finished (afaik to support buffered IO in the IO controller) will afford us a more meaningful reason to work to make cgroups' blkio controller actually work with bio-based devices like LVM's DM devices? I'm very much open to advice on how to proceed with investigating this integration work. Tejun, Vivek, anyone else: if you have advice on next steps for DM on this front _please_ yell, thanks! Mike -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
