[Qemu-block] Why qemu processes can bypass cgroup's blkio.weight ?

[Bob Chen]

Hello,

I want to achieve proportional IO sharing by using cgroup.

My qemu config is:     -drive file=$DISKFILe,if=none,format=qcow2,cache=none,aio=native -device virtio-blk-pci...

Test command inside vm is:     dd if=/dev/vdc of=/dev/null iflag=direct

Cgroup blkio weight of the qemu process is properly configured as well.

But no matter how change the proportion, such as vm1=400 and vm2=100, I can only get the equal IO speed.

Wondering cgroup blkio.weight or blkio.weight_device has no effect on qemu?

PS. cache=writethrough aio=threads is also tested, the same results.