Cray reported an stat performance degradation in master with older servers (pre < 2.4).

it's easy replicated with statmany tool, as now it's have only ~600 stats per second for same files.

after bisect search by Cray

Patrick Farrell: http://review.whamcloud.com/#/c/6460/8/lustre/mdc/mdc_locks.c
Patrick Farrell: That's the patch that my bisection suggests is the problem

after looking to logs - i see more getattr rpc's as should be in such situation.
so root cause of additional RPC's - patch tries to match PERM bit in lock for servers don't supported such feature, after disabling it - stat rate is restored.