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 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
