On Fri, Aug 12, 2011 at 1:06 PM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote: > On Fri, Aug 12, 2011 at 6:00 AM, Zhi Yong Wu <zwu.kernel@xxxxxxxxx> wrote: >> On Wed, Aug 10, 2011 at 7:00 PM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote: >>> On Wed, Aug 10, 2011 at 7:57 AM, Zhi Yong Wu <zwu.kernel@xxxxxxxxx> wrote: >>>> On Tue, Aug 9, 2011 at 11:19 PM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote: >>>>> On Tue, Aug 9, 2011 at 5:17 AM, Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx> wrote: >>>>>> Note: >>>>>> 1.) When bps/iops limits are specified to a small value such as 511 bytes/s, this VM will hang up. We are considering how to handle this senario. >>>>> >>>>> If an I/O request is larger than the limit itself then I think we >>>>> should let it through with a warning that the limit is too low. This >>>> If it will print a waring, it seems to be not a nice way, the >>>> throtting function will take no effect on this scenario. >>> >>> Setting the limit below the max request size is a misconfiguration. >>> It's a problem that the user needs to be aware of and fix, so a >>> warning is appropriate. Unfortunately the max request size is not >>> easy to determine from the block layer and may vary between guest >>> OSes, that's why we need to do something at runtime. >>> >>> We cannot leave this case unhandled because it results in the guest >>> timing out I/O without any information about the problem - that makes >>> it hard to troubleshoot for the user. Any other ideas on how to >>> handle this case? >> Can we constrain the io limits specified by the user? When the limits >> is smaller than some value such as 1MB/s, one error is provide to the >> user and remind he/her that the limits is too small. > > It would be an arbitrary limit because the maximum request size > depends on the storage interface or on the host block device. Guest > OSes may limit the max request size further. There is no single > constant that we can choose ahead of time. Any constant value risks > not allowing the user to set a small valid limit or being less than > the max request size and therefore causing I/O to stall again. Let us think at first. When anyone of us has some better idea, we will rediscuss this.:) > > Stefan > -- Regards, Zhi Yong Wu -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
