Solr search UI is very slow

When using the debug mode (debug=true in the URL) to display the time spend in Solr itself we usually end up with a number that is a very small fraction (for example 38ms spend in Solr and 400ms just to display the result) of the time spent displaying the whole things (even without the skin). The URL job is just to display the result and should not be so slow, it's a lot slower than the home page which contains Activity Stream...

Some elements:

• about 23% of the request is spend executing html macros (about 41 times) which makes the html macro probably deserve its own performance issue (a lot of work has been done to improve html macros and macros handling in general)
• half the time is spent displaying the facets
• with default setup a long time is also spent loading documents because many unexisting documents are filling the cache at each request (should be fixed by XWIKI-12046 and XWIKI-12118)