CP-44533 Add running vCPU and running domain of host into rrdd

[LunfanZhang]

This PR aims to add the number of running vCPU and running domain into rrdd:

1. For the running vCPUs, I derive this information from 'xenctrl.vcpuinfo', where the vCPU's state is marked as 'online' and 'not blocked'. Although we could calculate it based solely on the 'running' states, I find that 'online' and 'not blocked' covers a wider range of scenarios.
2. For the running domains, I straightforwardly derive this data from 'xenctrl.domaininfo', where the domain's state is indicated as 'running.
3. I convert the Dom0 memory_internal_free from B to KiB, due to the official document declare the unit of this attribution is KiB, see:
   

new test result:

[root@xrtuk-13-07 ~]# xe host-data-source-query data-source=running_vcpus
1.000000
[root@xrtuk-13-07 ~]# xe host-data-source-query data-source=running_domains
1.000000
[root@xrtuk-13-07 ~]# xe vm-data-source-query vm=14466515-ef55-43c7-a0ec-018994064f2e data-source=memory_internal_free
2191387.500000

[LunfanZhang]

I passed the check format locally, I don't know why it failed on the remote check. Is there anyone who has permission to retrigger check format again?

[psafont]

The local check fails because the formatter is not up-to-date, please update your local build environment, rebase your pull request on top of the latest master and retry

[lindig]

Keep it simple and avoid fancy comments that are difficult to reformat if needed.

[LunfanZhang]

Absolutely, it can be deleted.

[lindig]

Traditionally, condition is called pred or predicate.

[LunfanZhang]

I will refine it.

[lindig]

This creates garbage that could be avoided. We want to count elements in a list that fulfill a predicate.

List.fold_left (fun count (dom, _, _) -> if dom.Xenctrl.running then count +1 else count) 0 domains

[LunfanZhang]

Is it because of the way I used creates a new List? Sorry, I don't know much about Ocaml GC.

[lindig]

No problem. It's cheap to iterate over a lost and more expensive to create intermediate complex values like a new list. In my code I iterate over the list and carry a simple integer value.

[lindig]

In light of the discussion of count_running_domain, could this be done in a simpler, similar way? The predicate ctrl.Xenctrl.online && not ctrl.Xenctrl.blocked could be implemented in this function and not passed in from the outside and this would result in one compact function.

[LunfanZhang]

Some other statuses could be added in the future, such as ctrl.Xenctrl.blocked or ctrl.Xenctrl.running. Therefore, I believe keeping the count_running_domain will be beneficial for compatibility

[minglumlu]

The xc can be wrapped into pred (renamed to count_vcpus_in_domain).
So basically the functions could be:

let count_vcpus_in_domain domain =
  let dom, _, domid = domain in
  let f vcpu_id =
    let open Xenctrl in
    let vcpuinfo = domain_get_vcpuinfo xc domid vcpu_id in
    if vcpuinfo.online && not vcpuinfo.blocked then 1 else 0
  in
  sum 0 dom.Xenctrl.max_vcpu_id f
in
let vcpus =
  List.map count_vcpus_in_domain domains
  |> List.fold_left (+) 0
in

let count_running_domain domain =
  let dom, _, _ = domain in
  if dom.Xenctrl.running then 1 else 0
in
let running_domains =
  List.map count_running_domain domains
  |> List.fold_left (+) 0

[LunfanZhang]

I have reverted this part of change to the original to keep it simple.

[minglumlu]

From the comment, this is a fraction. But from the calculation, this seems a count number?

[LunfanZhang]

Fixed

[minglumlu]

From the comment, this is a fraction. But from the calculation, this seems a count number?

[LunfanZhang]

I could convert fraction -> int.
However, I still have a question. Even though I've set the type of this metric as int64, I'm still receiving decimal values, such as 1.333, when I query it. Is this due to the final display of this metric being the calculated average over a time range？

[minglumlu]

I understand the RRD will return a consolidated value:
https://docs.xenserver.com/en-us/xenserver/8/developer/sdk-guide/using-http.html#getting-xenserver-operational-metrics
You could try to change the Consolidation Functions (CF) to confirm this. By default it is average. But this should be done by RRD framework already.

[minglumlu]

Here I think the units requires a string of unit. Like "memory_total_kib" with units "KiB", how about "running_domains" with units "domains"?

[LunfanZhang]

Agree, I will use domains vcpus as the units.