Update patch set 1

Patch Set 1:

(5 comments)

Patch-set: 1
CC: Gerrit User 9708 <9708@4a232e18-c5a9-48ee-94c0-e04e7cca6543>

8487cb0bd57caf9f881457b38a5e77a6e88733cd

@@ -321,6 +321,91 @@
       "revId": "8487cb0bd57caf9f881457b38a5e77a6e88733cd",
       "serverId": "4a232e18-c5a9-48ee-94c0-e04e7cca6543"
     },
+    {
+      "unresolved": true,
+      "key": {
+        "uuid": "d3a4f5db_27ac96bc",
+        "filename": "specs/backlog/nova-dynamic-cpus.rst",
+        "patchSetId": 1
+      },
+      "lineNbr": 172,
+      "author": {
+        "id": 9708
+      },
+      "writtenOn": "2024-01-23T17:09:16Z",
+      "side": 1,
+      "message": "This means that with cpu_overhead_set some of the hypervisor cpus needs to be dedicated to the overhead and therefore cannot be used for vcpus. This will decreased the vcpu capacity of the hypervisor at least from scheduling perspective. I\u0027m not sure deployers will be happy with this capacity reduction.",
+      "revId": "8487cb0bd57caf9f881457b38a5e77a6e88733cd",
+      "serverId": "4a232e18-c5a9-48ee-94c0-e04e7cca6543"
+    },
+    {
+      "unresolved": true,
+      "key": {
+        "uuid": "b4e587d2_4351a44a",
+        "filename": "specs/backlog/nova-dynamic-cpus.rst",
+        "patchSetId": 1
+      },
+      "lineNbr": 187,
+      "author": {
+        "id": 9708
+      },
+      "writtenOn": "2024-01-23T17:09:16Z",
+      "side": 1,
+      "message": "I think this is the main change. And there are dragons here. Any time we tried to represent the same physical resource as two, independently consumable logical resources in placement we ended up introducing bugs. I don\u0027t say we cannot do this correctly but I do say that this is a dangerous move.\n\nE.g. \n* we deprecated support for configuring both the PF and its VFs via device_spec.\n* we are fixing bugs where a PGPU can provide different but mutually exclusive VGPU types.",
+      "revId": "8487cb0bd57caf9f881457b38a5e77a6e88733cd",
+      "serverId": "4a232e18-c5a9-48ee-94c0-e04e7cca6543"
+    },
+    {
+      "unresolved": true,
+      "key": {
+        "uuid": "582c0eaa_fd2194e9",
+        "filename": "specs/backlog/nova-dynamic-cpus.rst",
+        "patchSetId": 1
+      },
+      "lineNbr": 261,
+      "author": {
+        "id": 9708
+      },
+      "writtenOn": "2024-01-23T17:09:16Z",
+      "side": 1,
+      "message": "While you try to limit the fragmentation of the pin-able cpu cores via packing floating cores such fragmentation will manifest eventually via the creation and deletion of VMs with different flavors.\n\nE.g.:\n3 physical cores, allocation ratio 2.0. pcore_id : available_vcore_count \u003d {0:2, 1:2, 2:2}\n1. boot a VM with 2 vcpus -\u003e mapped to 0, 1, {0:1, 1:1, 2:2}\n2. boot a VM with 1 vcpu -\u003e mapped to 0 (0 is full now), {0:0, 1:1, 2:2}\n3. boot a VM with 2 vcpus -\u003e mapped to 1, 2 (as 0 is full but 1 still have a vcpu), {0:0, 1:0, 2:1} \n4. delete the VM with the 1 vcpu allocation. {0:1, 1:0, 2:1}\nAt this point we have a total allocation of 4 vcpus but it is spread to all 3 pcores. So logically we have space for a pinned core, but due to fragmentation we don\u0027t have the ability to allocate it. \n\nI don\u0027t think there is a fragmentation free algorithm. So either we live with the fact of fragmentation, or do some dynamic re-packing of the floating vcpus.",
+      "revId": "8487cb0bd57caf9f881457b38a5e77a6e88733cd",
+      "serverId": "4a232e18-c5a9-48ee-94c0-e04e7cca6543"
+    },
+    {
+      "unresolved": true,
+      "key": {
+        "uuid": "4b138557_1a3d4474",
+        "filename": "specs/backlog/nova-dynamic-cpus.rst",
+        "patchSetId": 1
+      },
+      "lineNbr": 445,
+      "author": {
+        "id": 9708
+      },
+      "writtenOn": "2024-01-23T17:09:16Z",
+      "side": 1,
+      "message": "This is probably not relevant but I noticed that in the proposed change if a host has available PCPUs then it will always have available VCPUs as a PCPU can be used as one or more VCPUs. However not vice versa. So there might be hosts with available VCPUs but no available PCPUs any more.",
+      "revId": "8487cb0bd57caf9f881457b38a5e77a6e88733cd",
+      "serverId": "4a232e18-c5a9-48ee-94c0-e04e7cca6543"
+    },
+    {
+      "unresolved": true,
+      "key": {
+        "uuid": "68f5599a_86df508f",
+        "filename": "specs/backlog/nova-dynamic-cpus.rst",
+        "patchSetId": 1
+      },
+      "lineNbr": 465,
+      "author": {
+        "id": 9708
+      },
+      "writtenOn": "2024-01-23T17:09:16Z",
+      "side": 1,
+      "message": "I don\u0027t see a way that placement would return a wrong allocation candidate due to the proposed change as the inventory of both logical resources are correctly tracked via changing the reserved value.",
+      "revId": "8487cb0bd57caf9f881457b38a5e77a6e88733cd",
+      "serverId": "4a232e18-c5a9-48ee-94c0-e04e7cca6543"
+    },
     {
       "unresolved": true,
       "key": {