Vivek Goyal wrote: > o Currently a request queue has got fixed number of request descriptors for > sync and async requests. Once the request descriptors are consumed, new > processes are put to sleep and they effectively become serialized. Because > sync and async queues are separate, async requests don't impact sync ones > but if one is looking for fairness between async requests, that is not > achievable if request queue descriptors become bottleneck. > > o Make request descriptor's per io group so that if there is lots of IO > going on in one cgroup, it does not impact the IO of other group. > > o This is just one relatively simple way of doing things. This patch will > probably change after the feedback. Folks have raised concerns that in > hierchical setup, child's request descriptors should be capped by parent's > request descriptors. May be we need to have per cgroup per device files > in cgroups where one can specify the upper limit of request descriptors > and whenever a cgroup is created one needs to assign request descritor > limit making sure total sum of child's request descriptor is not more than > of parent. > > I guess something like memory controller. Anyway, that would be the next > step. For the time being, we have implemented something simpler as follows. > > o This patch implements the per cgroup request descriptors. request pool per > queue is still common but every group will have its own wait list and its > own count of request descriptors allocated to that group for sync and async > queues. So effectively request_list becomes per io group property and not a > global request queue feature. > > o Currently one can define q->nr_requests to limit request descriptors > allocated for the queue. Now there is another tunable q->nr_group_requests > which controls the requests descriptr limit per group. q->nr_requests > supercedes q->nr_group_requests to make sure if there are lots of groups > present, we don't end up allocating too many request descriptors on the > queue. > Hi Vivek, In order to prevent q->nr_requests from becoming the bottle-neck of allocating requests, whether we can update nr_requests accordingly when allocating or removing a cgroup? -- Regards Gui Jianfeng -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
