tuning.md

@@ -91,16 +91,12 @@ Some of the OptimisationSwitches relevant for MPI/Parallel:
    to avoid race conditions. A value of 1 or greater can currently be
    used to enable an initial barrier.
 - `pbufs.tuning` *PstreamBuffers tuning* (default: -1)
-   * **value = -1 (default)** :
+   * **value = 0 (legacy PEX)** :
      use all-to-all to exchange buffer sizes,
      followed by point-to-point communication for the contents.
-   * **value = 0** :
+   * **value = 1 (hybrid PEX)** :
      use NBX to exchange buffer sizes,
      followed by point-to-point communication for the contents.
-   * **value = 1** :
-     use NBX exchange for the buffer contents (and sizes) directly.
-     This is not currently recommended until it has been much more
-     thoroughly tested.
 - `nPollProcInterfaces` *processor patch polling* (default: 0) <br>
    * **value = 0 (default)** :
      non-polling. Wait for all exchanges to complete before dispatching.
@@ -110,6 +106,11 @@ Some of the OptimisationSwitches relevant for MPI/Parallel:
    * **value >= 1** : deprecated (will be removed)
 
 
+***Caution***
+in OpenFOAM-v2306 the `pbufs.tuning` used slightly
+different values (-1 : legacy, 0 : hybrid).
+
+
 ### Comments on parallel tuning
 
 It is expected that large simulations with many geometry changes