doc: typo

doc/chapters/perf-optimization.texi

@@ -315,6 +315,6 @@ detailed in the next chapter. The various informations should be checked for.
   scheduler didn't assign tasks to them. Perhaps the performance model is bogus,
   check it (see @ref{Codelet performance}). Do all your codelets have a
   performance model?  When some of them don't, the schedulers switches to a
-  greedy algorithm which thus performs bad.
+  greedy algorithm which thus performs badly.
 @end itemize
 @end itemize