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. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- 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
