MiKTeX: pdftex -trace=...,...,... ???


I try the -trace option of the compilers (etex , pdfTeX) but
nothing seems to happen.

I hoped the trace and tracefile variables would output something !

My miktex.ini file is :

% ---------------------------------------------------------------------
max_print_line=90 ; width of the .log lines

error_line=90 ; width of the error .log lines (<= max_print_line)
half_error_line=75 ; width of the first error .log lines ( >=30 and <= error_line-15 )

tracefile=<some file>
% ---------------------------------------------------------------------

By the way, I found how to change the width of the .log lines :
-max-print-line = <Number of characters>

Thanks if you have any clue about trace and tracefile.
I read several MiKTeX manuals for different versions without success... too bad