On Mon, Oct 5, 2009 at 10:10 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > On Mon, Oct 05, 2009 at 11:55:35PM +0900, Ryo Tsuruta wrote: >> Hi Vivek, >> >> Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: >> > On Mon, Oct 05, 2009 at 07:38:08PM +0900, Ryo Tsuruta wrote: >> > > Hi, >> > > >> > > Munehiro Ikeda <m-ikeda@xxxxxxxxxxxxx> wrote: >> > > > Vivek Goyal wrote, on 10/01/2009 10:57 PM: >> > > > > Before finishing this mail, will throw a whacky idea in the ring. I was >> > > > > going through the request based dm-multipath paper. Will it make sense >> > > > > to implement request based dm-ioband? So basically we implement all the >> > > > > group scheduling in CFQ and let dm-ioband implement a request function >> > > > > to take the request and break it back into bios. This way we can keep >> > > > > all the group control at one place and also meet most of the requirements. >> > > > > >> > > > > So request based dm-ioband will have a request in hand once that request >> > > > > has passed group control and prio control. Because dm-ioband is a device >> > > > > mapper target, one can put it on higher level devices (practically taking >> > > > > CFQ at higher level device), and provide fairness there. One can also >> > > > > put it on those SSDs which don't use IO scheduler (this is kind of forcing >> > > > > them to use the IO scheduler.) >> > > > > >> > > > > I am sure that will be many issues but one big issue I could think of that >> > > > > CFQ thinks that there is one device beneath it and dipsatches requests >> > > > > from one queue (in case of idling) and that would kill parallelism at >> > > > > higher layer and throughput will suffer on many of the dm/md configurations. >> > > > > >> > > > > Thanks >> > > > > Vivek >> > > > >> > > > As long as using CFQ, your idea is reasonable for me. But how about for >> > > > other IO schedulers? In my understanding, one of the keys to guarantee >> > > > group isolation in your patch is to have per-group IO scheduler internal >> > > > queue even with as, deadline, and noop scheduler. I think this is >> > > > great idea, and to implement generic code for all IO schedulers was >> > > > concluded when we had so many IO scheduler specific proposals. >> > > > If we will still need per-group IO scheduler internal queues with >> > > > request-based dm-ioband, we have to modify elevator layer. It seems >> > > > out of scope of dm. >> > > > I might miss something... >> > > >> > > IIUC, the request based device-mapper could not break back a request >> > > into bio, so it could not work with block devices which don't use the >> > > IO scheduler. >> > > >> > >> > I think current request based multipath drvier does not do it but can't it >> > be implemented that requests are broken back into bio? >> >> I guess it would be hard to implement it, and we need to hold requests >> and throttle them at there and it would break the ordering by CFQ. >> >> > Anyway, I don't feel too strongly about this approach as it might >> > introduce more serialization at higher layer. >> >> Yes, I know it. >> >> > > How about adding a callback function to the higher level controller? >> > > CFQ calls it when the active queue runs out of time, then the higer >> > > level controller use it as a trigger or a hint to move IO group, so >> > > I think a time-based controller could be implemented at higher level. >> > > >> > >> > Adding a call back should not be a big issue. But that means you are >> > planning to run only one group at higher layer at one time and I think >> > that's the problem because than we are introducing serialization at higher >> > layer. So any higher level device mapper target which has multiple >> > physical disks under it, we might be underutilizing these even more and >> > take a big hit on overall throughput. >> > >> > The whole design of doing proportional weight at lower layer is optimial >> > usage of system. >> >> But I think that the higher level approch makes easy to configure >> against striped software raid devices. > > How does it make easier to configure in case of higher level controller? > > In case of lower level design, one just have to create cgroups and assign > weights to cgroups. This mininum step will be required in higher level > controller also. (Even if you get rid of dm-ioband device setup step). > >> If one would like to >> combine some physical disks into one logical device like a dm-linear, >> I think one should map the IO controller on each physical device and >> combine them into one logical device. >> > > In fact this sounds like a more complicated step where one has to setup > one dm-ioband device on top of each physical device. But I am assuming > that this will go away once you move to per reuqest queue like implementation. > > I think it should be same in principal as my initial implementation of IO > controller on request queue and I stopped development on it because of FIFO > dispatch. > > So you seem to be suggesting that you will move dm-ioband to request queue > so that setting up additional device setup is gone. You will also enable > it to do time based groups policy, so that we don't run into issues on > seeky media. Will also enable dispatch from one group only at a time so > that we don't run into isolation issues and can do time accounting > accruately. Will that approach solve the problem of doing bandwidth control on logical devices? What would be the advantages compared to Vivek's current patches? > > If yes, then that has the potential to solve the issue. At higher layer one > can think of enabling size of IO/number of IO policy both for proportional > BW and max BW type of control. At lower level one can enable pure time > based control on seeky media. > > I think this will still left with the issue of prio with-in group as group > control is separate and you will not be maintatinig separate queues for > each process. Similarly you will also have isseus with read vs write > ratios as IO schedulers underneath change. > > So I will be curious to see that implementation. > >> > > My requirements for IO controller are: >> > > - Implement s a higher level controller, which is located at block >> > > layer and bio is grabbed in generic_make_request(). >> > >> > How are you planning to handle the issue of buffered writes Andrew raised? >> >> I think that it would be better to use the higher-level controller >> along with the memory controller and have limits memory usage for each >> cgroup. And as Kamezawa-san said, having limits of dirty pages would >> be better, too. >> > > Ok. So if we plan to co-mount memory controller with per memory group > dirty_ratio implemented, that can work with both higher level as well as > low level controller. Not sure if we also require some kind of a per > memory group flusher thread infrastructure also to make sure higher weight > group gets more job done. > >> > > - Can work with any type of IO scheduler. >> > > - Can work with any type of block devices. >> > > - Support multiple policies, proportional wegiht, max rate, time >> > > based, ans so on. >> > > >> > > The IO controller mini-summit will be held in next week, and I'm >> > > looking forard to meet you all and discuss about IO controller. >> > > https://sourceforge.net/apps/trac/ioband/wiki/iosummit >> > >> > Is there a new version of dm-ioband now where you have solved the issue of >> > sync/async dispatch with-in group? Before meeting at mini-summit, I am >> > trying to run some tests and come up with numbers so that we have more >> > clear picture of pros/cons. >> >> Yes, I've released new versions of dm-ioband and blkio-cgroup. The new >> dm-ioband handles sync/async IO requests separately and >> the write-starve-read issue you pointed out is fixed. I would >> appreciate it if you would try them. >> http://sourceforge.net/projects/ioband/files/ > > Cool. Will get to testing it. > > Thanks > Vivek > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
