diff options
Diffstat (limited to 'qemu-options.hx')
| -rw-r--r-- | qemu-options.hx | 49 |
1 files changed, 38 insertions, 11 deletions
diff --git a/qemu-options.hx b/qemu-options.hx index 04c259157a..b5efa648ba 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -405,15 +405,22 @@ SRST -numa node,nodeid=0 -numa node,nodeid=1 \ -numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1 - Legacy '\ ``mem``\ ' assigns a given RAM amount to a node (not supported - for 5.1 and newer machine types). '\ ``memdev``\ ' assigns RAM from - a given memory backend device to a node. If '\ ``mem``\ ' and - '\ ``memdev``\ ' are omitted in all nodes, RAM is split equally between them. - - - '\ ``mem``\ ' and '\ ``memdev``\ ' are mutually exclusive. - Furthermore, if one node uses '\ ``memdev``\ ', all of them have to - use it. + '\ ``memdev``\ ' option assigns RAM from a given memory backend + device to a node. It is recommended to use '\ ``memdev``\ ' option + over legacy '\ ``mem``\ ' option. This is because '\ ``memdev``\ ' + option provides better performance and more control over the + backend's RAM (e.g. '\ ``prealloc``\ ' parameter of + '\ ``-memory-backend-ram``\ ' allows memory preallocation). + + For compatibility reasons, legacy '\ ``mem``\ ' option is + supported in 5.0 and older machine types. Note that '\ ``mem``\ ' + and '\ ``memdev``\ ' are mutually exclusive. If one node uses + '\ ``memdev``\ ', the rest nodes have to use '\ ``memdev``\ ' + option, and vice versa. + + Users must specify memory for all NUMA nodes by '\ ``memdev``\ ' + (or legacy '\ ``mem``\ ' if available). In QEMU 5.2, the support + for '\ ``-numa node``\ ' without memory specified was removed. '\ ``initiator``\ ' is an additional option that points to an initiator NUMA node that has best performance (the lowest latency or @@ -1143,10 +1150,22 @@ have gone through several iterations as the feature set and complexity of the block layer have grown. Many online guides to QEMU often reference older and deprecated options, which can lead to confusion. -The recommended modern way to describe disks is to use a combination of +The most explicit way to describe disks is to use a combination of ``-device`` to specify the hardware device and ``-blockdev`` to describe the backend. The device defines what the guest sees and the -backend describes how QEMU handles the data. +backend describes how QEMU handles the data. It is the only guaranteed +stable interface for describing block devices and as such is +recommended for management tools and scripting. + +The ``-drive`` option combines the device and backend into a single +command line option which is a more human friendly. There is however no +interface stability guarantee although some older board models still +need updating to work with the modern blockdev forms. + +Older options like ``-hda`` are essentially macros which expand into +``-drive`` options for various drive interfaces. The original forms +bake in a lot of assumptions from the days when QEMU was emulating a +legacy PC, they are not recommended for modern configurations. ERST @@ -1639,6 +1658,14 @@ SRST the raw disk image you use is not written back. You can however force the write back by pressing C-a s (see the :ref:`disk images` chapter in the System Emulation Users Guide). + + .. warning:: + snapshot is incompatible with ``-blockdev`` (instead use qemu-img + to manually create snapshot images to attach to your blockdev). + If you have mixed ``-blockdev`` and ``-drive`` declarations you + can use the 'snapshot' property on your drive declarations + instead of this global option. + ERST DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev, |