On Tue, May 31, 2011 at 03:19:56PM +0100, Daniel P. Berrange wrote: > On Tue, May 31, 2011 at 10:10:37AM -0400, Vivek Goyal wrote: > > On Tue, May 31, 2011 at 02:56:46PM +0100, Daniel P. Berrange wrote: > > > On Tue, May 31, 2011 at 09:45:37AM -0400, Vivek Goyal wrote: > > > > On Mon, May 30, 2011 at 01:09:23PM +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. > > > > > > > > > > > > > Hi Zhiyong, > > > > > > > > Why not use kernel blkio controller for this and why reinvent the wheel > > > > and implement the feature again in qemu? > > > > > > The finest level of granularity offered by cgroups apply limits per QEMU > > > process. So the blkio controller can't be used to apply controls directly > > > to individual disks used by QEMU, only the VM as a whole. > > > > So are multiple VMs using same disk. Then put multiple VMs in same > > cgroup and apply the limit on that disk. > > > > Or if you want to put a system wide limit on a disk, then put all > > VMs in root cgroup and put limit on root cgroups. > > > > I fail to understand what's the exact requirement here. I thought > > the biggest use case was isolation one VM from other which might > > be sharing same device. Hence we were interested in putting > > per VM limit on disk and not a system wide limit on disk (independent > > of VM). > > No, it isn't about putting limits on a disk independant of a VM. It is > about one VM having multiple disks, and wanting to set different policies > for each of its virtual disks. eg > > qemu-kvm -drive file=/dev/sda1 -drive file=/dev/sdb3 > > and wanting to say that sda1 is limited to 10 MB/s, while sdb3 is > limited to 50 MB/s. You can't do that kind of thing with cgroups, > because it can only control the entire process, not individual > resources within the process. With IO controller you can do that. Limits are "per cgroup per disk". So once you have put a VM in a cgroup, you can specify two differnt limits for two disk for that cgroup. There are 4 relevant files per cgroup. blkio.throttle.read_bps_device blkio.throttle.write_bps_device blkio.throttle.read_iops_device blkio.throttle.write_iops_device And syntax of these files is. device_major:device_minor <rate_limit> Ex. 8:16 1024000 This means from a specified cgroup, on disk with major:minor 8:16, don't allow read BW higher than 1024000 bytes per second. Thanks Vivek -- 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
