On Tue, Mar 1, 2011 at 5:01 AM, ya su <suya94...@gmail.com> wrote:
>   kvm start with disk image on nfs server, when nfs server can not be
> reached, monitor will be blocked. I change io_thread to SCHED_RR
> policy, it will work unfluently waiting for disk read/write timeout.

There are some synchronous disk image reads that can put qemu-kvm to
sleep until NFS responds or errors.  For example, when starting
hw/virtio-blk.c calls bdrv_guess_geometry() which may invoke
bdrv_read().

Once the VM is running and you're using virtio-blk then disk I/O
should be asynchronous.  There are some synchronous cases to do with
migration, snapshotting, etc where we wait for outstanding aio
requests.  Again this can block qemu-kvm.

So in short, there's no easy way to avoid blocking the VM in all cases
today.  You should find, however, that normal read/write operation to
a running VM does not cause qemu-kvm to sleep.

Stefan
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