Commit d9243af2 authored by Dariusz Stojaczyk's avatar Dariusz Stojaczyk Committed by Jim Harris
Browse files

doc/virtio: minor doc updates 



Reworded some sentences, updated current limitation
list, and dropped the outdated `Multiqueue` section.

Change-Id: Id57777430f00b80c68cadf4c600e4ec89fa3c4e0
Signed-off-by: default avatarDariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/397082


Reviewed-by: default avatarPawel Wodkowski <pawelx.wodkowski@intel.com>
Tested-by: default avatarSPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: default avatarDaniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: default avatarJim Harris <james.r.harris@intel.com>
parent 11130d09

doc/virtio.md

+5 −14
Original line number Diff line number Diff line
@@ -12,11 +12,6 @@ controller. The host, after sending I/O to the real drive, will put the response 
back into the Virtio queue. Then, the response is received by the Virtio SCSI

driver.



The driver, just like the SPDK @ref vhost, is using pollers instead of standard

interrupts to check for an I/O response. It bypasses kernel interrupt and context

switching overhead of QEMU and guest kernel, significantly boosting the overall

I/O performance.



Virtio SCSI driver supports two different usage models:

* PCI - This is the standard mode of operation when used in a guest virtual

machine, where QEMU has presented the virtio-scsi controller as a virtual
@@ -24,18 +19,14 @@ PCI device. 
* User vhost - Can be used to connect to a vhost-scsi socket directly on the

same host.



# Multiqueue {#virtio_multiqueue}



The Virtio SCSI controller will automatically manage virtio queue distribution.

Currently each thread doing an I/O on a single bdev will get an exclusive queue.

Multi-threaded I/O on bdevs from a single Virtio-SCSI controller is not supported.

The driver, just like the SPDK @ref vhost, is using pollers instead of standard

interrupts to check for an I/O response. If used inside a VM, it bypasses interrupt

and context switching overhead of QEMU and guest kernel, significantly boosting

the overall I/O performance.



# Limitations {#virtio_limitations}



The Virtio SCSI driver is still experimental.  Current implementation has many

limitations:

Current Virtio-SCSI implementation has a couple of limitations:

 * supports only up to 8 hugepages (implies only 1GB sized pages are practical)

 * single LUN per target

 * only SPDK vhost-scsi controllers supported
 
 * no RPC

 * no multi-threaded I/O for single-queue virtio devices