projects / ceph.git / blame
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1 | .. SPDX-License-Identifier: BSD-3-Clause |
| 2 | Copyright(c) 2010-2017 Intel Corporation. | |
| 3 | ||
| 4 | Vhost_scsi Sample Application | |
| 5 | ============================= | |
| 6 | ||
| 7 | The vhost_scsi sample application implemented a simple SCSI block device, | |
| 8 | which used as the backend of Qemu vhost-user-scsi device. Users can extend | |
| 9 | the exist example to use other type of block device(e.g. AIO) besides | |
| 10 | memory based block device. Similar with vhost-user-net device, the sample | |
| 11 | application used domain socket to communicate with Qemu, and the virtio | |
| 12 | ring was processed by vhost_scsi sample application. | |
| 13 | ||
| 14 | The sample application reuse lots codes from SPDK(Storage Performance | |
| 15 | Development Kit, https://github.com/spdk/spdk) vhost-user-scsi target, | |
| 16 | for DPDK vhost library used in storage area, user can take SPDK as | |
| 17 | reference as well. | |
| 18 | ||
| 19 | Testing steps | |
| 20 | ------------- | |
| 21 | ||
| 22 | This section shows the steps how to start a VM with the block device as | |
| 23 | fast data path for critical application. | |
| 24 | ||
| 25 | Compiling the Application | |
| 26 | ------------------------- | |
| 27 | ||
| 28 | To compile the sample application see :doc:`compiling`. | |
| 29 | ||
| 30 | The application is located in the ``examples`` sub-directory. | |
| 31 | ||
| 32 | You will also need to build DPDK both on the host and inside the guest | |
| 33 | ||
| 34 | Start the vhost_scsi example | |
| 35 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
| 36 | ||
| 37 | .. code-block:: console | |
| 38 | ||
| 39 | ./vhost_scsi -m 1024 | |
| 40 | ||
| 41 | .. _vhost_scsi_app_run_vm: | |
| 42 | ||
| 43 | Start the VM | |
| 44 | ~~~~~~~~~~~~ | |
| 45 | ||
| 46 | .. code-block:: console | |
| 47 | ||
| 48 | qemu-system-x86_64 -machine accel=kvm \ | |
| 49 | -m $mem -object memory-backend-file,id=mem,size=$mem,\ | |
| 50 | mem-path=/dev/hugepages,share=on -numa node,memdev=mem \ | |
| 51 | -drive file=os.img,if=none,id=disk \ | |
| 52 | -device ide-hd,drive=disk,bootindex=0 \ | |
| 53 | -chardev socket,id=char0,path=/tmp/vhost.socket \ | |
| 54 | -device vhost-user-scsi-pci,chardev=char0,bootindex=2 \ | |
| 55 | ... | |
| 56 | ||
| 57 | .. note:: | |
| 58 | You must check whether your Qemu can support "vhost-user-scsi" or not, | |
| 59 | Qemu v2.10 or newer version is required. | |
| 60 | ||
| 61 | Vhost_scsi Common Issues | |
| 62 | ------------------------ | |
| 63 | ||
| 64 | * vhost_scsi can not start with block size 512 Bytes: | |
| 65 | ||
| 9f95a23c | 66 | Currently DPDK vhost library was designed for NET device(although the APIs |
| 11fdf7f2 TL |
67 | are generic now), for 512 Bytes block device, Qemu BIOS(x86 BIOS Enhanced |
| 68 | Disk Device) will enumerate all block device and do some IOs to those block | |
| 69 | devices with 512 Bytes sector size. DPDK vhost library can not process such | |
| 70 | scenarios(both BIOS and OS will enumerate the block device), so as a | |
| 71 | workaround, the vhost_scsi example application hardcoded the block size | |
| 72 | with 4096 Bytes. | |
| 73 | ||
| 74 | * vhost_scsi can only support the block device as fast data disk(non OS image): | |
| 75 | ||
| 76 | Make sure ``bootindex=2`` Qemu option is given to vhost-user-scsi-pci device. | |
| 77 |