d9243af2b1
Reworded some sentences, updated current limitation list, and dropped the outdated `Multiqueue` section. Change-Id: Id57777430f00b80c68cadf4c600e4ec89fa3c4e0 Signed-off-by: Dariusz Stojaczyk <dariuszx.stojaczyk@intel.com> Reviewed-on: https://review.gerrithub.io/397082 Reviewed-by: Pawel Wodkowski <pawelx.wodkowski@intel.com> Tested-by: SPDK Automated Test System <sys_sgsw@intel.com> Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com> Reviewed-by: Jim Harris <james.r.harris@intel.com>
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Virtio SCSI driver
Introduction
Virtio SCSI driver is an initiator for SPDK @ref vhost application. The driver allows any SPDK app to connect to another SPDK instance exposing 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:
- 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 PCI device.
- 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 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
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