On Wed, Jul 18, 2012 at 04:07:27PM +0100, Stefan Hajnoczi wrote:
> 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.
Do you have any numbers at all?
> 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
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