Many processes blocked at ProcArrayLock

Test configuration:
Hardware:
    4P intel server, 60 core 120 hard thread.
    Memory:512G
    SSD:2.4T

PG:
max_connections = 160            # (change requires restart)
shared_buffers = 32GB
work_mem = 128MB
maintenance_work_mem = 32MB
bgwriter_delay = 100ms            # 10-10000ms between rounds
bgwriter_lru_maxpages = 200        # 0-1000 max buffers written/round
bgwriter_lru_multiplier = 2.0        # 0-10.0 multipler on buffers scanned/round
wal_level = minimal            # minimal, archive, or hot_standby
wal_buffers = 256MB            # min 32kB, -1 sets based on shared_buffers
autovacuum = off
checkpoint_timeout=60min
checkpoint_segments = 1000
archive_mode = off
synchronous_commit = off
fsync = off
full_page_writes = off


We use tpcc and pgbench to test postgresql 9.4beat2 performance. And we found the tps/tpmc could not increase with the
terminalincrease. The detail information is in attachment. 

Many processes is blocked, I dump the call stack, and found these processes is blocked at: ProcArrayLock. 60% processes
isblocked in ProcArrayEndTransaction with ProcArrayLock EXCLUSIVE, 20% is in GetSnapshotData with ProcArrayLock SHARED.
Otherslocks like XLogFlush and WALInsertLock are not very heavy. 

Is there any way we solve this problem?