CG: note that CPU threads affect cell count in regtests (issue 3257)

diff --git a/Documentation/contributor/regressions.itexi b/Documentation/contributor/regressions.itexi
index c155a8b923ad946a6beec6aaa2772eb26353935c..8b600465f5ffbfda13c6b774b862846fab55d258 100644 (file)
--- a/Documentation/contributor/regressions.itexi
+++ b/Documentation/contributor/regressions.itexi
@@ -135,6 +135,11 @@ something is suspicious!
 @item
 Profile files: give information about
 TODO?  I don't know what they're for.
+Apparently they give some information about CPU usage.  If you got
+tons of changes in cell counts, this probably means that you compiled
+@code{make test-baseline} with a different amount of CPU threads than
+@code{make check}. Try redoing tests from scratch with the same
+number of threads each time -- see @ref{Saving time with the -j option}.
 
 @end itemize