diff --git a/src/tef/dune b/src/tef/dune
index acacd95..89b8e9a 100644
--- a/src/tef/dune
+++ b/src/tef/dune
@@ -3,7 +3,4 @@
   (name trace_tef)
   (public_name trace-tef)
   (synopsis "Simple and lightweight tracing using TEF/Catapult format, in-process")
-  (libraries trace.core mtime mtime.clock.os atomic unix threads
-             (select relax_.ml from
-                     (base-domain -> relax_.real.ml)
-                     ( -> relax_.dummy.ml))))
+  (libraries trace.core trace.private.util mtime mtime.clock.os atomic unix threads))
diff --git a/src/tef/trace_tef.ml b/src/tef/trace_tef.ml
index aed6653..bd36ecb 100644
--- a/src/tef/trace_tef.ml
+++ b/src/tef/trace_tef.ml
@@ -1,4 +1,5 @@
 open Trace_core
+open Trace_private_util
 module A = Trace_core.Internal_.Atomic_
 
 module Mock_ = struct
@@ -14,7 +15,7 @@ end
 let counter = Mtime_clock.counter ()
 
 (** Now, in microseconds *)
-let now_us () : float =
+let[@inline] now_us () : float =
   if !Mock_.enabled then
     Mock_.now_us ()
   else (
@@ -22,16 +23,6 @@ let now_us () : float =
     Mtime.Span.to_float_ns t /. 1e3
   )
 
-let protect ~finally f =
-  try
-    let x = f () in
-    finally ();
-    x
-  with exn ->
-    let bt = Printexc.get_raw_backtrace () in
-    finally ();
-    Printexc.raise_with_backtrace exn bt
-
 let on_tracing_error = ref (fun s -> Printf.eprintf "trace-tef error: %s\n%!" s)
 
 type event =
@@ -144,7 +135,7 @@ module Writer = struct
 
   let with_ ~out f =
     let writer = create ~out () in
-    protect ~finally:(fun () -> close writer) (fun () -> f writer)
+    Fun.protect ~finally:(fun () -> close writer) (fun () -> f writer)
 
   let[@inline] flush (self : t) : unit = flush self.oc
 
@@ -499,7 +490,7 @@ let setup ?(out = `Env) () =
 
 let with_setup ?out () f =
   setup ?out ();
-  protect ~finally:Trace_core.shutdown f
+  Fun.protect ~finally:Trace_core.shutdown f
 
 module Internal_ = struct
   let mock_all_ () = Mock_.enabled := true
diff --git a/src/tef/b_queue.ml b/src/util/b_queue.ml
similarity index 100%
rename from src/tef/b_queue.ml
rename to src/util/b_queue.ml
diff --git a/src/tef/b_queue.mli b/src/util/b_queue.mli
similarity index 100%
rename from src/tef/b_queue.mli
rename to src/util/b_queue.mli
diff --git a/src/tef/relax_.dummy.ml b/src/util/cpu_relax.dummy.ml
similarity index 100%
rename from src/tef/relax_.dummy.ml
rename to src/util/cpu_relax.dummy.ml
diff --git a/src/util/cpu_relax.mli b/src/util/cpu_relax.mli
new file mode 100644
index 0000000..17542a8
--- /dev/null
+++ b/src/util/cpu_relax.mli
@@ -0,0 +1 @@
+val cpu_relax : unit -> unit
diff --git a/src/tef/relax_.real.ml b/src/util/cpu_relax.real.ml
similarity index 100%
rename from src/tef/relax_.real.ml
rename to src/util/cpu_relax.real.ml
diff --git a/src/util/dune b/src/util/dune
new file mode 100644
index 0000000..fc5fb6f
--- /dev/null
+++ b/src/util/dune
@@ -0,0 +1,9 @@
+
+(library
+  (public_name trace.private.util)
+  (synopsis "internal utilities for trace. No guarantees of stability.")
+  (name trace_private_util)
+  (libraries trace.core mtime mtime.clock.os atomic unix threads
+             (select cpu_relax.ml from
+                     (base-domain -> cpu_relax.real.ml)
+                     ( -> cpu_relax.dummy.ml))))
diff --git a/src/tef/mpsc_bag.ml b/src/util/mpsc_bag.ml
similarity index 95%
rename from src/tef/mpsc_bag.ml
rename to src/util/mpsc_bag.ml
index 004e8f5..453357f 100644
--- a/src/tef/mpsc_bag.ml
+++ b/src/util/mpsc_bag.ml
@@ -11,7 +11,7 @@ module Backoff = struct
 
   let once (b : t) : t =
     for _i = 1 to b do
-      Relax_.cpu_relax ()
+      Cpu_relax.cpu_relax ()
     done;
     min (b * 2) 256
 end
diff --git a/src/tef/mpsc_bag.mli b/src/util/mpsc_bag.mli
similarity index 100%
rename from src/tef/mpsc_bag.mli
rename to src/util/mpsc_bag.mli