Filter module performance issue

Those filters which is disabled should not be listed sometimes. is not very specific about what part of the UI this would impact. If one does not list a disabled filter, how do they enable it?

Without any benchmarking, this is not a major issue. Changing check_markup() would be an API change.

+++ b/modules/filter/filter.module
@@ -688,20 +688,25 @@ function _filter_format_is_cacheable($format) {
+function filter_list_format($format_id, $all = TRUE) {

This is a change to a function signature -- needs documentation change to match.

Also removing random tags.

+++ b/modules/filter/filter.module
@@ -683,25 +685,34 @@ function _filter_format_is_cacheable($format) {
+  $filters = &drupal_static(__FUNCTION__.$all, array());

It's occurred to me that changing the name of a static is technically changing the API -- other parts of the core or contrib may be clearing this static. So I don't think that's going to work.

Overall, how much of a performance gain is this going to produce? How often, typically, are filters disabled in a format?

I don't understand the proposed performance gain either, especially since check_markup() already has code to avoid processing disabled filters (as it must; otherwise it would be a huge bug if disabled filters were being applied to the text):

  // Give filters the chance to escape HTML-like data such as code or formulas.
  foreach ($filters as $name => $filter) {
    if ($filter->status && isset($filter_info[$name]['prepare callback']) && function_exists($filter_info[$name]['prepare callback'])) {

(notice the $filter->status check in the if statement)

So doesn't that mean there is no real performance gain here except for making the foreach() loop a little shorter (which is a very tiny micro-optimization)? There would also be fewer filters loaded from the database, I suppose; however, that is offset by the fact that there are now two static caches within filter_list_format() rather than one, so in some cases there would be an extra database query per page request that was never there before.