Update feature/perf from master

[edwintorok]

Continuing from #6208

The conflict resolution can be reviewed with:
git log --remerge-diff -1 8b8af637c4bf21974405c2e509491180442a5a47

diff --git a/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml
remerge CONFLICT (content): Merge conflict in ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml
index 7bace30dae..27cf306995 100644
--- a/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml
+++ b/ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler.ml
@@ -33,49 +33,8 @@ let (queue : t Ipq.t) = Ipq.create 50 queue_default

 let lock = Mutex.create ()

-<<<<<<< 6589d9aa6e (Xapi thread classification - part 2 (#6154))
 let add_to_queue_span name ty start_span newfunc =
   let ( ++ ) = Mtime.Span.add in
-||||||| 4f3f08f8fb
-module Clock = struct
-  let span s = Mtime.Span.of_uint64_ns (Int64.of_float (s *. 1e9))
-
-  let span_to_s span =
-    Mtime.Span.to_uint64_ns span |> Int64.to_float |> fun ns -> ns /. 1e9
-
-  let add_span clock secs =
-    (* return mix or max available value if the add overflows *)
-    match Mtime.add_span clock (span secs) with
-    | Some t ->
-        t
-    | None when secs > 0. ->
-        Mtime.max_stamp
-    | None ->
-        Mtime.min_stamp
-end
-
-let add_to_queue name ty start newfunc =
-  let ( ++ ) = Clock.add_span in
-=======
-module Clock = struct
-  let span s = Mtime.Span.of_uint64_ns (Int64.of_float (s *. 1e9))
-
-  let span_to_s span = Mtime.Span.to_float_ns span |> fun ns -> ns /. 1e9
-
-  let add_span clock secs =
-    (* return mix or max available value if the add overflows *)
-    match Mtime.add_span clock (span secs) with
-    | Some t ->
-        t
-    | None when secs > 0. ->
-        Mtime.max_stamp
-    | None ->
-        Mtime.min_stamp
-end
-
-let add_to_queue name ty start newfunc =
-  let ( ++ ) = Clock.add_span in
->>>>>>> 8c9b754481 (SDK fixes including CP-53003 (#6210))
   let item =
     {
       Ipq.ev= {func= newfunc; ty; name}

This code got deleted in feature/perf 6b02474, where span_to_s got replaced with Clock.Timer.span_to_s, and changed in master by e68cda7.
Both achieve the same result: span_to_s uses Mtime.Span.to_float_ns, except the commit on feature/perf also removes code duplication by reusing the other clock module.