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doc/vhost: update example parameter when starting VM

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Some Linux distributions reports kernel panic using the same
command line as we suggested in this document, that's because
number of IO queues is bigger than number of CPUs, so here
just fix it and added a comment on the number of IO queues
parameter.

See issues #1295 and #1737.

Change-Id: Ie1e18d5e83a80523f71d98b8761d13a8d57cc9ab
Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/7852
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Ziye Yang <ziye.yang@intel.com>
Reviewed-by: John Kariuki <John.K.Kariuki@intel.com>
Reviewed-by: <dongx.yi@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
This commit is contained in:
Changpeng Liu 2021-05-12 21:10:54 +08:00 committed by Jim Harris
parent d424e2449a
commit 7e9d5ae123
1 changed files with 6 additions and 2 deletions
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doc/vhost.md
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@ -280,9 +280,9 @@ host:~# taskset -c 2,3 qemu-system-x86_64 \
-drive file=guest_os_image.qcow2,if=none,id=disk \
-device ide-hd,drive=disk,bootindex=0 \
-chardev socket,id=spdk_vhost_scsi0,path=/var/tmp/vhost.0 \
-device vhost-user-scsi-pci,id=scsi0,chardev=spdk_vhost_scsi0,num_queues=4 \
-device vhost-user-scsi-pci,id=scsi0,chardev=spdk_vhost_scsi0,num_queues=2 \
-chardev socket,id=spdk_vhost_blk0,path=/var/tmp/vhost.1 \
-device vhost-user-blk-pci,chardev=spdk_vhost_blk0,num-queues=4
-device vhost-user-blk-pci,chardev=spdk_vhost_blk0,num-queues=2
~~~
Please note the following two commands are run on the guest VM.
@ -331,6 +331,10 @@ to set `num_queues=4` to saturate physical device. Adding too many queues might
vhost performance degradation if many vhost devices are used because each device will require
additional `num_queues` to be polled.
Some Linux distributions report a kernel panic when starting the VM if the number of I/O queues
specified via the `num-queues` parameter is greater than number of vCPUs. If you need to use
more I/O queues than vCPUs, check that your OS image supports that configuration.
## Hot-attach/hot-detach {#vhost_hotattach}
Hotplug/hotremove within a vhost controller is called hot-attach/detach. This is to