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doc/virtio: minor updates

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Reflect three changes:
 * Virtio now works with Linux and QEMU vhost targets
 * The Virtio library was separated from bdev modules
 * Virtio Blk bdev module has been added

Change-Id: I7d3075ca863a1142b3ddcc4d18e982f3b7c72202
Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/405288
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
This commit is contained in:
Dariusz Stojaczyk 2018-03-26 08:10:07 +02:00 committed by Jim Harris
parent 07526d85ef
commit 36506448d4
1 changed files with 10 additions and 16 deletions
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doc/virtio.md
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# Virtio SCSI driver {#virtio} # Virtio driver {#virtio}
# Introduction {#virtio_intro} # Introduction {#virtio_intro}
Virtio SCSI driver is an initiator for SPDK @ref vhost application. The SPDK Virtio driver is a C library that allows communicating with Virtio devices.
driver allows any SPDK app to connect to another SPDK instance exposing It allows any SPDK application to become an initiator for (SPDK) vhost targets.
a vhost-scsi device. The driver will enumerate targets on the device (which acts
as a SCSI controller) and create *virtual* bdevs usable by any SPDK application.
Sending an I/O request to the Virtio SCSI bdev will put the request data into
a Virtio queue that is processed by the host SPDK app exposing the
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.
Virtio SCSI driver supports two different usage models: The driver supports two different usage models:
* PCI - This is the standard mode of operation when used in a guest virtual * 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 machine, where QEMU has presented the virtio controller as a virtual PCI device.
PCI device. * vhost-user - Can be used to connect to a vhost socket directly on the same host.
* User vhost - Can be used to connect to a vhost-scsi socket directly on the
same host.
The driver, just like the SPDK @ref vhost, is using pollers instead of standard 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 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 and context switching overhead of QEMU and guest kernel, significantly boosting
the overall I/O performance. the overall I/O performance.
This Virtio library is currently used to implement two bdev modules:
@ref bdev_config_virtio_scsi and Virtio Blk. These modules will export generic
SPDK block devices usable by any other SPDK application.
# Limitations {#virtio_limitations} # Limitations {#virtio_limitations}
Current Virtio-SCSI implementation has a couple of limitations: Current Virtio-SCSI implementation has a couple of limitations:
* supports only up to 8 hugepages (implies only 1GB sized pages are practical) * supports only up to 8 hugepages (implies only 1GB sized pages are practical)
* single LUN per target * single LUN per target
* only SPDK vhost-scsi controllers supported