there's no cpu or memory contention. We increased the max workers thread from 2000 to 4000.But we are still seeing issue. Suddently the worker thread count reaches the max value and sql server doesn't respond. when look at the wait_types it shows sos_scheduler_yield and XE_BUFFERMGR_FREEBUF_EVENT are very high. Not able to figure out why the server is behaving weirdly.

server config: windows server 2008 r2 sp1

sql server : sql server 2008 sp3