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Date: Mon, 20 Jul 2009 22:55:31 -0700 From: Nauman Rafique <nauman@...gle.com> To: Gui Jianfeng <guijianfeng@...fujitsu.com> Cc: Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org, dm-devel@...hat.com, jens.axboe@...cle.com, dpshah@...gle.com, lizf@...fujitsu.com, mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it, ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com, taka@...inux.co.jp, jmoyer@...hat.com, dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com, righi.andrea@...il.com, m-ikeda@...jp.nec.com, jbaron@...hat.com, agk@...hat.com, snitzer@...hat.com, akpm@...ux-foundation.org, peterz@...radead.org Subject: Re: [PATCH 21/25] io-controller: Per cgroup request descriptor support On Mon, Jul 20, 2009 at 10:37 PM, Gui Jianfeng<guijianfeng@...fujitsu.com> wrote: > 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? Vivek, I agree with Gui here. In fact, it does not make much sense to keep the nr_requests limit if we already have per cgroup limit in place. This change also simplifies code quite a bit, as we can get rid of all that sleep_on_global logic. > > -- > Regards > Gui Jianfeng > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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