Hello Stefan,
On 11/15/2012 11:18 PM, Stefan Hajnoczi wrote:
> This series adds the -device virtio-blk-pci,x-data-plane=on property that
> enables a high performance I/O codepath. A dedicated thread is used to
> process
> virtio-blk requests outside the global mutex and without going through the
> QEMU
> block layer.
>
> Khoa Huynh <k...@us.ibm.com> reported an increase from 140,000 IOPS to 600,000
> IOPS for a single VM using virtio-blk-data-plane in July:
>
> http://comments.gmane.org/gmane.comp.emulators.kvm.devel/94580
>
> The virtio-blk-data-plane approach was originally presented at Linux Plumbers
> Conference 2010. The following slides contain a brief overview:
>
>
> http://linuxplumbersconf.org/2010/ocw/system/presentations/651/original/Optimizing_the_QEMU_Storage_Stack.pdf
>
> 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 irqfd from the dedicated thread.
>
> To try it out:
>
> qemu -drive if=none,id=drive0,cache=none,aio=native,format=raw,file=...
> -device virtio-blk-pci,drive=drive0,scsi=off,x-data-plane=on
Is this the latest dataplane bits:
(git://github.com/stefanha/qemu.git virtio-blk-data-plane)
commit 7872075c24fa01c925d4f41faa9d04ce69bf5328
Author: Stefan Hajnoczi <stefa...@redhat.com>
Date: Wed Nov 14 15:45:38 2012 +0100
virtio-blk: add x-data-plane=on|off performance feature
With this commit on a ramdisk based box, I am seeing about 10K IOPS with
x-data-plane on and 90K IOPS with x-data-plane off.
Any ideas?
Command line I used:
IMG=/dev/ram0
x86_64-softmmu/qemu-system-x86_64 \
-drive file=/root/img/sid.img,if=ide \
-drive file=${IMG},if=none,cache=none,aio=native,id=disk1 -device
virtio-blk-pci,x-data-plane=off,drive=disk1,scsi=off \
-kernel $KERNEL -append "root=/dev/sdb1 console=tty0" \
-L /tmp/qemu-dataplane/share/qemu/ -nographic -vnc :0 -enable-kvm -m
2048 -smp 4 -cpu qemu64,+x2apic -M pc
>
> Limitations:
> * Only format=raw is supported
> * Live migration is not supported
> * Block jobs, hot unplug, and other operations fail with -EBUSY
> * I/O throttling limits are ignored
> * Only Linux hosts are supported due to Linux AIO usage
>
> The code has reached a stage where I feel it is ready to merge. Users have
> been playing with it for some time and want the significant performance boost.
>
> We are refactoring QEMU to get rid of the global mutex. I believe that
> virtio-blk-data-plane can eventually become the default mode of operation.
>
> Instead of waiting for global mutex removal efforts to finish, I want to use
> virtio-blk-data-plane as an example device for AioContext and threaded hw
> dispatch refactoring. This means:
>
> 1. When the block layer can bind to an AioContext and execute I/O outside the
> global mutex, virtio-blk-data-plane can use this (and gain image format
> support).
>
> 2. When hw dispatch no longer needs the global mutex we can use hw/virtio.c
> again and perhaps run a pool of iothreads instead of dedicated data plane
> threads.
>
> But in the meantime, I have cleaned up the virtio-blk-data-plane code so that
> it can be merged as an experimental feature.
>
> Changes from the RFC v9:
> * Add x-data-plane=on|off option and coexist with regular virtio-blk code
> * Create thread from BH so it inherits iothread cpusets
> * Drain requests on vm_stop() so stopped guest does not access image file
> * Add migration blocker
> * Add bdrv_in_use() to prevent block jobs and other operations that can
> interfere
> * Drop IOQueue request merging for simplicity
> * Drop ioctl interrupt injection and always use irqfd for simplicity
> * Major cleanup to split up source files
> * Rebase from qemu-kvm.git onto qemu.git
> * Address Michael Tsirkin's review comments
>
> Stefan Hajnoczi (7):
> raw-posix: add raw_get_aio_fd() for virtio-blk-data-plane
> configure: add CONFIG_VIRTIO_BLK_DATA_PLANE
> dataplane: add virtqueue vring code
> dataplane: add event loop
> dataplane: add Linux AIO request queue
> dataplane: add virtio-blk data plane code
> virtio-blk: add x-data-plane=on|off performance feature
>
> block.h | 9 +
> block/raw-posix.c | 34 ++++
> configure | 21 +++
> hw/Makefile.objs | 2 +-
> hw/dataplane/Makefile.objs | 3 +
> hw/dataplane/event-poll.c | 109 ++++++++++++
> hw/dataplane/event-poll.h | 40 +++++
> hw/dataplane/ioq.c | 118 +++++++++++++
> hw/dataplane/ioq.h | 57 +++++++
> hw/dataplane/virtio-blk.c | 414
> +++++++++++++++++++++++++++++++++++++++++++++
> hw/dataplane/virtio-blk.h | 41 +++++
> hw/dataplane/vring.c | 321 +++++++++++++++++++++++++++++++++++
> hw/dataplane/vring.h | 54 ++++++
> hw/virtio-blk.c | 59 ++++++-
> hw/virtio-blk.h | 1 +
> hw/virtio-pci.c | 3 +
> trace-events | 9 +
> 17 files changed, 1293 insertions(+), 2 deletions(-)
> create mode 100644 hw/dataplane/Makefile.objs
> create mode 100644 hw/dataplane/event-poll.c
> create mode 100644 hw/dataplane/event-poll.h
> create mode 100644 hw/dataplane/ioq.c
> create mode 100644 hw/dataplane/ioq.h
> create mode 100644 hw/dataplane/virtio-blk.c
> create mode 100644 hw/dataplane/virtio-blk.h
> create mode 100644 hw/dataplane/vring.c
> create mode 100644 hw/dataplane/vring.h
>
--
Asias
