Commit 7e9d5ae1 authored by Changpeng Liu's avatar Changpeng Liu Committed by Jim Harris
Browse files

doc/vhost: update example parameter when starting VM 



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: default avatarChangpeng Liu <changpeng.liu@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/7852


Tested-by: default avatarSPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: default avatarZiye Yang <ziye.yang@intel.com>
Reviewed-by: default avatarJohn Kariuki <John.K.Kariuki@intel.com>
Reviewed-by: default avatar <dongx.yi@intel.com>
Reviewed-by: default avatarTomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: default avatarJim Harris <james.r.harris@intel.com>
parent d424e244

doc/vhost.md

+6 −2
Original line number Diff line number Diff line
@@ -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