Vivek Goyal wrote: > On Thu, Sep 18, 2008 at 04:37:41PM +0200, Andrea Righi wrote: >> Vivek Goyal wrote: >>> On Thu, Sep 18, 2008 at 09:04:18PM +0900, Ryo Tsuruta wrote: >>>> Hi All, >>>> >>>> I have got excellent results of dm-ioband, that controls the disk I/O >>>> bandwidth even when it accepts delayed write requests. >>>> >>>> In this time, I ran some benchmarks with a high-end storage. The >>>> reason was to avoid a performance bottleneck due to mechanical factors >>>> such as seek time. >>>> >>>> You can see the details of the benchmarks at: >>>> http://people.valinux.co.jp/~ryov/dm-ioband/hps/ >>>> >>> Hi Ryo, >>> >>> I had a query about dm-ioband patches. IIUC, dm-ioband patches will break >>> the notion of process priority in CFQ because now dm-ioband device will >>> hold the bio and issue these to lower layers later based on which bio's >>> become ready. Hence actual bio submitting context might be different and >>> because cfq derives the io_context from current task, it will be broken. >>> >>> To mitigate that problem, we probably need to implement Fernando's >>> suggestion of putting io_context pointer in bio. >>> >>> Have you already done something to solve this issue? >>> >>> Secondly, why do we have to create an additional dm-ioband device for >>> every device we want to control using rules. This looks little odd >>> atleast to me. Can't we keep it in line with rest of the controllers >>> where task grouping takes place using cgroup and rules are specified in >>> cgroup itself (The way Andrea Righi does for io-throttling patches)? >>> >>> To avoid creation of stacking another device (dm-ioband) on top of every >>> device we want to subject to rules, I was thinking of maintaining an >>> rb-tree per request queue. Requests will first go into this rb-tree upon >>> __make_request() and then will filter down to elevator associated with the >>> queue (if there is one). This will provide us the control of releasing >>> bio's to elevaor based on policies (proportional weight, max bandwidth >>> etc) and no need of stacking additional block device. >>> >>> I am working on some experimental proof of concept patches. It will take >>> some time though. >>> >>> I was thinking of following. >>> >>> - Adopt the Andrea Righi's style of specifying rules for devices and >>> group the tasks using cgroups. >>> >>> - To begin with, adopt dm-ioband's approach of proportional bandwidth >>> controller. It makes sense to me limit the bandwidth usage only in >>> case of contention. If there is really a need to limit max bandwidth, >>> then probably we can do something to implement additional rules or >>> implement some policy switcher where user can decide what kind of >>> policies need to be implemented. >>> >>> - Get rid of dm-ioband and instead buffer requests on an rb-tree on every >>> request queue which is controlled by some kind of cgroup rules. >>> >>> It would be good to discuss above approach now whether it makes sense or >>> not. I think it is kind of fusion of io-throttling and dm-ioband patches >>> with additional idea of doing io-control just above elevator on the request >>> queue using an rb-tree. >> Thanks Vivek. All sounds reasonable to me and I think this is be the right way >> to proceed. >> >> I'll try to design and implement your rb-tree per request-queue idea into my >> io-throttle controller, maybe we can reuse it also for a more generic solution. >> Feel free to send me your experimental proof of concept if you want, even if >> it's not yet complete, I can review it, test and contribute. > > Currently I have taken code from bio-cgroup to implement cgroups and to > provide functionality to associate a bio to a cgroup. I need this to be > able to queue the bio's at right node in the rb-tree and then also to be > able to take a decision when is the right time to release few requests. > > Right now in crude implementation, I am working on making system boot. > Once patches are at least in little bit working shape, I will send it to you > to have a look. > > Thanks > Vivek I wonder... wouldn't be simpler to just use the memory controller to retrieve this information starting from struct page? I mean, following this path (in short, obviously using the appropriate interfaces for locking and referencing the different objects): cgrp = page->page_cgroup->mem_cgroup->css.cgroup Once you get the cgrp it's very easy to use the corresponding controller structure. Actually, this is how I'm doing in cgroup-io-throttle to associate a bio to a cgroup. What other functionalities/advantages bio-cgroup provide in addition to that? Thanks, -Andrea -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
