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-rw-r--r--api-guide/source/accelerator-support.rst30
1 files changed, 28 insertions, 2 deletions
diff --git a/api-guide/source/accelerator-support.rst b/api-guide/source/accelerator-support.rst
index d6f91f05e9..cf9f185273 100644
--- a/api-guide/source/accelerator-support.rst
+++ b/api-guide/source/accelerator-support.rst
@@ -10,8 +10,9 @@ To launch servers with accelerators, the administrator (or an user with
appropriate privileges) must do the following:
* Create a device profile in Cyborg, which specifies what accelerator
- resources need to be provisioned. (See `Cyborg device profiles API
- <https://docs.openstack.org/api-ref/accelerator/v2/index.html#device-profiles>`_.
+ resources need to be provisioned. (See `Cyborg device profiles API`_.)
+
+ .. _`Cyborg device profiles API`: https://docs.openstack.org/api-ref/accelerator/v2/index.html#device-profiles
* Set the device profile name as an extra spec in a chosen flavor,
with this syntax:
@@ -54,3 +55,28 @@ below:
Some operations, such as lock and unlock, work as they are effectively
no-ops for accelerators.
+
+Caveats
+-------
+
+.. note::
+
+ This information is correct as of the 21.0.0 Ussuri release. Where
+ improvements have been made or issues fixed, they are noted per item.
+
+For nested resource providers:
+
+* Creating servers with accelerators provisioned with the Cyborg service, if
+ a flavor asks for resources that are provided by nested Resource Provider
+ inventories (e.g. vGPU) and the user wants multi-create (i.e. say --max 2)
+ then the scheduler could be returning a NoValidHosts exception even if each
+ nested Resource Provider can support at least one specific instance, if the
+ total wanted capacity is not supported by only one nested Resource Provider.
+ (See `bug 1874664 <https://bugs.launchpad.net/nova/+bug/1874664>`_.)
+
+ For example, creating servers with accelerators provisioned with the Cyborg
+ service, if two children RPs have 4 vGPU inventories each:
+
+ - You can ask for a device profile in the flavor with 2 vGPU with --max 2.
+ - But you can't ask for a device profile in the flavor with 4 vGPU and
+ --max 2.