Re: [PATCH 5/5] virtio-scsi: introduce multiqueue support

Il 04/09/2012 13:09, Michael S. Tsirkin ha scritto:

quoted

quoted

    queuecommand on CPU #0         queuecommand #2 on CPU #1
  --------------------------------------------------------------
    atomic_inc_return(...) == 1
                                   atomic_inc_return(...) == 2
                                   virtscsi_queuecommand to queue #1
    tgt->req_vq = queue #0
    virtscsi_queuecommand to queue #0

then two requests are issued to different queues without a quiescent
point in the middle.

What happens then? Does this break correctness?

Yes, requests to the same target should be processed in FIFO order, or
you have things like a flush issued before the write it was supposed to
flush.  This is why I can only change the queue when there is no request
pending.

Paolo