From: Rik van Riel Subject: Re: [PATCH 20/23] io-controller: Per cgroup request descriptor support Date: Mon, 31 Aug 2009 13:54:44 -0400 Message-ID: <4A9C0E64.8000401@redhat.com> References: <1251495072-7780-1-git-send-email-vgoyal@redhat.com> <1251495072-7780-21-git-send-email-vgoyal@redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1251495072-7780-21-git-send-email-vgoyal@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Vivek Goyal Cc: dhaval@linux.vnet.ibm.com, peterz@infradead.org, dm-devel@redhat.com, dpshah@google.com, jens.axboe@oracle.com, agk@redhat.com, balbir@linux.vnet.ibm.com, paolo.valente@unimore.it, jmarchan@redhat.com, guijianfeng@cn.fujitsu.com, fernando@oss.ntt.co.jp, mikew@google.com, jmoyer@redhat.com, nauman@google.com, mingo@elte.hu, m-ikeda@ds.jp.nec.com, lizf@cn.fujitsu.com, fchecconi@gmail.com, s-uchida@ap.jp.nec.com, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, righi.andrea@gmail.com, torvalds@linux-foundation.org List-Id: dm-devel.ids 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 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. > > Signed-off-by: Nauman Rafique > Signed-off-by: Vivek Goyal Acked-by: Rik van Riel