[Qemu-devel] [RFC v9 00/27] virtio: virtio-blk data plane

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

This series implements a dedicated thread for virtio-blk processing using Linux
AIO for raw image files only.  It is based on qemu-kvm.git a0bc8c3 and somewhat
old but I wanted to share it on the list since it has been mentioned on mailing
lists and IRC recently.

These patches can be used for benchmarking and discussion about how to improve
block performance.  Paolo Bonzini has also worked in this area and might want
to share his patches.

The basic approach is:
1. Each virtio-blk device has a thread dedicated to handling ioeventfd
   signalling when the guest kicks the virtqueue.
2. Requests are processed without going through the QEMU block layer using
   Linux AIO directly.
3. Completion interrupts are injected via ioctl from the dedicated thread.

The series also contains request merging as a bdrv_aio_multiwrite() equivalent.
This was only to get a comparison against the QEMU block layer and I would drop
it for other types of analysis.

The effect of this series is that O_DIRECT Linux AIO on raw files can bypass
the QEMU global mutex and block layer.  This means higher performance.

A cleaned up version of this approach could be added to QEMU as a raw O_DIRECT
Linux AIO fast path.  Image file formats, protocols, and other block layer
features are not supported by virtio-blk-data-plane.

Git repo:
http://repo.or.cz/w/qemu-kvm/stefanha.git/shortlog/refs/heads/virtio-blk-data-plane

Stefan Hajnoczi (27):
  virtio-blk: Remove virtqueue request handling code
  virtio-blk: Set up host notifier for data plane
  virtio-blk: Data plane thread event loop
  virtio-blk: Map vring
  virtio-blk: Do cheapest possible memory mapping
  virtio-blk: Take PCI memory range into account
  virtio-blk: Put dataplane code into its own directory
  virtio-blk: Read requests from the vring
  virtio-blk: Add Linux AIO queue
  virtio-blk: Stop data plane thread cleanly
  virtio-blk: Indirect vring and flush support
  virtio-blk: Add workaround for BUG_ON() dependency in virtio_ring.h
  virtio-blk: Increase max requests for indirect vring
  virtio-blk: Use pthreads instead of qemu-thread
  notifier: Add a function to set the notifier
  virtio-blk: Kick data plane thread using event notifier set
  virtio-blk: Use guest notifier to raise interrupts
  virtio-blk: Call ioctl() directly instead of irqfd
  virtio-blk: Disable guest->host notifies while processing vring
  virtio-blk: Add ioscheduler to detect mergable requests
  virtio-blk: Add basic request merging
  virtio-blk: Fix request merging
  virtio-blk: Stub out SCSI commands
  virtio-blk: fix incorrect length
  msix: fix irqchip breakage in msix_try_notify_from_thread()
  msix: use upstream kvm_irqchip_set_irq()
  virtio-blk: add EVENT_IDX support to dataplane

 event_notifier.c          |    7 +
 event_notifier.h          |    1 +
 hw/dataplane/event-poll.h |  116 +++++++
 hw/dataplane/ioq.h        |  128 ++++++++
 hw/dataplane/iosched.h    |   97 ++++++
 hw/dataplane/vring.h      |  334 ++++++++++++++++++++
 hw/msix.c                 |   15 +
 hw/msix.h                 |    1 +
 hw/virtio-blk.c           |  753 +++++++++++++++++++++------------------------
 hw/virtio-pci.c           |    8 +
 hw/virtio.c               |    9 +
 hw/virtio.h               |    3 +
 12 files changed, 1074 insertions(+), 398 deletions(-)
 create mode 100644 hw/dataplane/event-poll.h
 create mode 100644 hw/dataplane/ioq.h
 create mode 100644 hw/dataplane/iosched.h
 create mode 100644 hw/dataplane/vring.h

-- 
1.7.10.4