Hi, On Mon, 2011-05-30 at 13:09 +0800, Zhi Yong Wu wrote: > Hello, all, > > I have prepared to work on a feature called "Disk I/O limits" for > qemu-kvm projeect. > This feature will enable the user to cap disk I/O amount performed by a > VM.It is important for some storage resources to be shared among multi-VMs. > As you've known, if some of VMs are doing excessive disk I/O, they will hurt > the performance of other VMs. > > More detail is available here: > http://wiki.qemu.org/Features/DiskIOLimits > > 1.) Why we need per-drive disk I/O limits > As you've known, for linux, cgroup blkio-controller has supported I/O > throttling on block devices. More importantly, there is no single mechanism > for disk I/O throttling across all underlying storage types (image file, LVM, > NFS, Ceph) and for some types there is no way to throttle at all. > > Disk I/O limits feature introduces QEMU block layer I/O limits together > with command-line and QMP interfaces for configuring limits. This allows I/O > limits to be imposed across all underlying storage types using a single > interface. > > 2.) How disk I/O limits will be implemented > QEMU block layer will introduce a per-drive disk I/O request queue for > those disks whose "disk I/O limits" feature is enabled. It can control disk > I/O limits individually for each disk when multiple disks are attached to a > VM, and enable use cases like unlimited local disk access but shared storage > access with limits. > In mutliple I/O threads scenario, when an application in a VM issues a > block I/O request, this request will be intercepted by QEMU block layer, then > it will calculate disk runtime I/O rate and determine if it has go beyond its > limits. If yes, this I/O request will enqueue to that introduced queue; > otherwise it will be serviced. > > 3.) How the users enable and play with it > QEMU -drive option will be extended so that disk I/O limits can be > specified on its command line, such as -drive [iops=xxx,][throughput=xxx] or > -drive [iops_rd=xxx,][iops_wr=xxx,][throughput=xxx] etc. When this argument > is specified, it means that "disk I/O limits" feature is enabled for this > drive disk. > The feature will also provide users with the ability to change per-drive > disk I/O limits at runtime using QMP commands.
I'm wondering if you've considered adding a 'burst' parameter - something which will not limit (or limit less) the io ops or the throughput for the first 'x' ms in a given time window. > Regards, > > Zhiyong Wu > -- Sasha.
