Re: FW: cgroup blkio.weight working, but not for KVM guests

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Oct 23, 2012 at 04:48:13PM -0600, Ben Clay wrote:
> Since this is not an issue, I guess another source of problems could be that
> all the virtio threads attached to this domain are not being placed within
> the cgroup.  I will look through libvirt to see if they're setting the
> guest's process's cgroup classification as sticky (I can't imagine they
> wouldn't be), but this raises another question: are virtio kernel threads
> child processes of the guest's main process?

Virtio kernel threads?

Depend on the qemu-kvm -drive ...,aio=native|threads setting you should
either see:

1. For aio=native QEMU uses the Linux AIO API.  I think this results in
   kernel threads that process I/O on behalf of the userspace process.

2. For aio=threads QEMU uses its own userspace threadpool to call
   preadv(2)/pwritev(2).  These threads are spawned from QEMU's
   "iothread" event loop.

I suggest you try switching between aio=native and aio=threads to check
if this causes the result you have been seeing.

> Are you aware of any other factor which I should be considering here?

No, but I haven't played with the cgroups blkio controller much.

Stefan