Solution : https://service.sap.com/sap/support/notes/1224599 (SAP Service marketplace login required)
Key words : 
suitable operating system tools, parameter wdisp/http/use_pool_for_new_conn, parameter cm/keep_alive, performance problems occur, runtime significantly increases, back-end icm, sap web dispatcher, terms use_pool_for_new_conn, web dispatcher, patch level 7
Related Notes : 
       
| 1177804 | |
| 1170353 | Security update: SAP Web Dispatcher | 
| 888889 | Automatic checks for security notes using RSECNOTE |