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virtio-scsi: add iothread-vq-mapping parameter

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Allow virtio-scsi virtqueues to be assigned to different IOThreads. This
makes it possible to take advantage of host multi-queue block layer
scalability by assigning virtqueues that have affinity with vCPUs to
different IOThreads that have affinity with host CPUs. The same feature
was introduced for virtio-blk in the past:
https://developers.redhat.com/articles/2024/09/05/scaling-virtio-blk-disk-io-iothread-virtqueue-mapping

Here are fio randread 4k iodepth=64 results from a 4 vCPU guest with an
Intel P4800X SSD:
iothreads IOPS
------------------------------
1         189576
2         312698
4         346744

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20250311132616.1049687-12-stefanha@redhat.com>
Tested-by: Peter Krempa <pkrempa@redhat.com>
[kwolf: Updated 051 output, virtio-scsi can now use any iothread]
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2025-03-11 21:26:14 +08:00 • committed by Kevin Wolf
parent b50629c335
commit 2e8e18c2e4
4 changed files with 108 additions and 52 deletions
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2
tests/qemu-iotests/051.pc.out
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@ -181,7 +181,7 @@ QEMU X.Y.Z monitor - type 'help' for more information
Testing: -drive file=TEST_DIR/t.qcow2,if=none,node-name=disk -object iothread,id=thread0 -device virtio-scsi,iothread=thread0,id=virtio-scsi0 -device scsi-hd,bus=virtio-scsi0.0,drive=disk,share-rw=on -device virtio-scsi,id=virtio-scsi1 -device scsi-hd,bus=virtio-scsi1.0,drive=disk,share-rw=on
QEMU X.Y.Z monitor - type 'help' for more information
(qemu) QEMU_PROG: -device scsi-hd,bus=virtio-scsi1.0,drive=disk,share-rw=on: Cannot change iothread of active block backend
(qemu) quit
Testing: -drive file=TEST_DIR/t.qcow2,if=none,node-name=disk -object iothread,id=thread0 -device virtio-scsi,iothread=thread0,id=virtio-scsi0 -device scsi-hd,bus=virtio-scsi0.0,drive=disk,share-rw=on -device virtio-blk-pci,drive=disk,iothread=thread0,share-rw=on
QEMU X.Y.Z monitor - type 'help' for more information