CP-53642: change default NUMA placement policy to best-effort

We've seen that using the policy can be up to 10% faster than using any is some
workflows, while not observing workflows that were negatively affected. The
policy per VM can always be change if need be.

Note that currently sometime the best-effort falls back to the same behaviour,
especially when restarting on starting more than one VM at a time. This needs
xen patches to be fixed:
https://lore.kernel.org/xen-devel/[email protected]/T/#ma1246e352ea3cce71c7ddc26d1329a368548b3b2

Now the deprecated numa-placement configuration option for xenopsd does nothing.
It was exclusively used to enable Best_effort, since now it's the default,
there's no point in setting the option. It's value depends on whether the
default option is best_effort or not, as per the spec.

Signed-off-by: Pau Ruiz Safont <[email protected]>

Author: psafont

ocaml/xenopsd/lib/xenops_server.ml

@@ -3472,9 +3472,9 @@ module VIF = struct
       ()
 end
 
-let default_numa_affinity_policy = ref Xenops_interface.Host.Any
+let default_numa_affinity_policy = ref Xenops_interface.Host.Best_effort
 
-let numa_placement = ref Xenops_interface.Host.Any
+let numa_placement = ref !default_numa_affinity_policy
 
 let string_of_numa_affinity_policy =
   Xenops_interface.Host.(function Any -> "any" | Best_effort -> "best-effort")

ocaml/xenopsd/lib/xenopsd.ml

@@ -59,8 +59,6 @@ let feature_flags_path = ref "/etc/xenserver/features.d"
 
 let pvinpvh_xen_cmdline = ref "pv-shim console=xen"
 
-let numa_placement_compat = ref false
-
 (* O(N^2) operations, until we get a xenstore cache, so use a small number here *)
 let vm_guest_agent_xenstore_quota = ref 128
 
@@ -242,8 +240,11 @@ let options =
     , "Command line for the inner-xen for PV-in-PVH guests"
     )
   ; ( "numa-placement"
-    , Arg.Bool (fun x -> numa_placement_compat := x)
-    , (fun () -> string_of_bool !numa_placement_compat)
+    , Arg.Bool (fun _ -> ())
+    , (fun () ->
+        string_of_bool
+          (!Xenops_server.default_numa_affinity_policy = Best_effort)
+      )
     , "NUMA-aware placement of VMs (deprecated, use XAPI setting)"
     )
   ; ( "pci-quarantine"

ocaml/xenopsd/xc/xenops_server_xen.ml

@@ -5294,8 +5294,6 @@ let init () =
         {Xs_protocol.ACL.owner= 0; other= Xs_protocol.ACL.READ; acl= []}
   ) ;
   Device.Backend.init () ;
-  Xenops_server.default_numa_affinity_policy :=
-    if !Xenopsd.numa_placement_compat then Best_effort else Any ;
   info "Default NUMA affinity policy is '%s'"
     Xenops_server.(string_of_numa_affinity_policy !default_numa_affinity_policy) ;
   Xenops_server.numa_placement := !Xenops_server.default_numa_affinity_policy ;