4 threads is probably not ideal for a 24 core system
both memcached and ep-engine changes were merged into the master branch.
assigning to Pavel to assist with functional validation in addition to performance validation.
Please notice that MB-10307 (mentioned above by Anil) has nothing to do with number of memcached threads.
And btw, MEMCACHED_NUM_CPUS is pretty confusing variable for number of threads.
The "correct" way to tune this parameter for the 3.0 series is through the configuration file passed to memcached with the -C argument, and through the "threads" setting as described in https://github.com/membase/memcached/blob/master/man/man4/memcached.json.4.txt#L17 . According to Alks comment on https://www.couchbase.com/issues/browse/MB-10330 there is a way to set this through /diag/eval (but he hasn't answerred my question if this is a public and documented interface as I've asked about in the bug report (which would invalidate the bug report)).