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Subject[PATCH 0/5] Multiqueue virtio-scsi
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Hi all,

this series adds multiqueue support to the virtio-scsi driver, based
on Jason Wang's work on virtio-net. It uses a simple queue steering
algorithm that expects one queue per CPU. LUNs in the same target always
use the same queue (so that commands are not reordered); queue switching
occurs when the request being queued is the only one for the target.
Also based on Jason's patches, the virtqueue affinity is set so that
each CPU is associated to one virtqueue.

I tested the patches with fio, using up to 32 virtio-scsi disks backed
by tmpfs on the host, and 1 LUN per target.

FIO configuration
-----------------
[global]
rw=read
bsrange=4k-64k
ioengine=libaio
direct=1
iodepth=4
loops=20
overall bandwidth (MB/s)
-----------------
# of targets single-queue multi-queue, 4 VCPUs multi-queue, 8 VCPUs
1 540 626 599
2 795 965 925
4 997 1376 1500
8 1136 2130 2060
16 1440 2269 2474
24 1408 2179 2436
32 1515 1978 2319

(These numbers for single-queue are with 4 VCPUs, but the impact of adding
more VCPUs is very limited).

avg bandwidth per LUN (MB/s)
---------------------
# of targets single-queue multi-queue, 4 VCPUs multi-queue, 8 VCPUs
1 540 626 599
2 397 482 462
4 249 344 375
8 142 266 257
16 90 141 154
24 58 90 101
32 47 61 72

Testing this may require an irqbalance daemon that is built from git,
due to http://code.google.com/p/irqbalance/issues/detail?id=37.
Alternatively you can just set the affinity manually in /proc.

Rusty, can you please give your Acked-by to the first two patches?

Jason Wang (2):
virtio-ring: move queue_index to vring_virtqueue
virtio: introduce an API to set affinity for a virtqueue

Paolo Bonzini (3):
virtio-scsi: allocate target pointers in a separate memory block
virtio-scsi: pass struct virtio_scsi to virtqueue completion function
virtio-scsi: introduce multiqueue support

drivers/lguest/lguest_device.c | 1 +
drivers/remoteproc/remoteproc_virtio.c | 1 +
drivers/s390/kvm/kvm_virtio.c | 1 +
drivers/scsi/virtio_scsi.c | 200 ++++++++++++++++++++++++--------
drivers/virtio/virtio_mmio.c | 11 +-
drivers/virtio/virtio_pci.c | 58 ++++++++-
drivers/virtio/virtio_ring.c | 17 +++
include/linux/virtio.h | 4 +
include/linux/virtio_config.h | 21 ++++
9 files changed, 253 insertions(+), 61 deletions(-)


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