Hi Luca,
On 08/04/2022 09:45, Luca Fancellu wrote:
diff --git a/docs/misc/arm/device-tree/cpupools.txt
b/docs/misc/arm/device-tree/cpupools.txt
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+Boot time cpupools
+==================
+
+When BOOT_TIME_CPUPOOLS is enabled in the Xen configuration, it is possible to
+create cpupools during boot phase by specifying them in the device tree.
+ACPI is not supported for this feature.
+
+Cpupools specification nodes shall be direct childs of /chosen node.
+Each cpupool node contains the following properties:
+
+- compatible (mandatory)
+
+ Must always include the compatiblity string: "xen,cpupool".
+
+- cpupool-cpus (mandatory)
+
+ Must be a list of device tree phandle to nodes describing cpus (e.g. having
+ device_type = "cpu"), it can't be empty.
+
+- cpupool-sched (optional)
+
+ Must be a string having the name of a Xen scheduler. Check the sched=<...>
+ boot argument for allowed values [1]. When this property is omitted, the
Xen
+ default scheduler will be used.
+
+
+Constraints
+===========
+
+If no cpupools are specified, all cpus will be assigned to one cpupool
+implicitly created (Pool-0).
+
+If cpupools node are specified, but not every cpu brought up by Xen is
assigned,
+all the not assigned cpu will be assigned to an additional cpupool.
+
+If a cpu is assigned to a cpupool, but it's not brought up correctly, Xen will
+stop.
+
+The boot cpu must be assigned to Pool-0, so the cpupool containing that core
+will become Pool-0 automatically.
+
+
+Examples
+========
+
+A system having two types of core, the following device tree specification will
+instruct Xen to have two cpupools:
+
+- The cpupool with id 0 will have 4 cpus assigned.
+- The cpupool with id 1 will have 2 cpus assigned.
AFAIK, there are no guarantee that Xen will parse cpupool_a first. So it
would be possible that the ID are inverted here.
This could happen if you want to keep the boot CPU in pool 0 and it is
not cpu@0 (some bootloaders allows you to change the boot CPU).
Also, here you write "The cpupool with id X" but ...
+A system having the cpupools specification below will instruct Xen to have
three
+cpupools:
+
+- The cpupool Pool-0 will have 2 cpus assigned.
+- The cpupool Pool-1 will have 2 cpus assigned.
+- The cpupool Pool-2 will have 2 cpus assigned (created by Xen with all the not
+ assigned cpus a53_3 and a53_4).
here you write "The cpupool Pool-X". Can you be consistent?
On a separate topic, I think dom0_max_vcpus() needs to be updated to by
default (i.e when opt_dom0_max_vcpus == 0) the number of vCPUs match the
number of vCPUs in the cpupool (I think 0) used to created dom0.
Cheers,
--
Julien Grall
