tutorials: use a specific version of starpu for the package starpu-fxt

contents/tutorials/2019-11-HPNS-Inria/index.html

@@ -844,9 +844,17 @@ Guix command to use it.
 </p>
 
 <tt><pre>
-$ guix environment --pure starpu-fxt --ad-hoc starpu-fxt grep coreutils emacs vim less gv -- /bin/bash --norc
+$ guix environment --pure starpu-fxt --ad-hoc starpu-fxt grep coreutils emacs vim less gv --with-commit=starpu-fxt=3cc33c3cc85eae5dbc0f4b0ddc9291e3409287b2 -- /bin/bash --norc
 </pre></tt>
 
+<p>
+  The Guix package <tt>starpu-fxt</tt> is currently based on the
+  version 1.3.3 of StarPU which has a bug which leads to the creation
+  of huge trace files. This has been fixed but not released yet, we
+  hence use the Guix parameter <tt>--with-commit</tt> to indicate a
+  specific commit for StarPU. This will no longer be needed after the
+  next StarPU release and the upgrade of the Guix package.
+</p>
 <!--
 <p>
 To use the version of StarPU compiled with FxT support, you need to recompile