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