This test with heavy write load, 3 GB cache, shows 4-5 seconds of 0 throughput at the end of a checkpoint.

• At the end of the pause numerous operations report >4s latency (from "mongod max logged query" graph).
• System CPU utilization and context switch rate are not high during the pause, so this is not due to SERVER-16662 (as that had been fixed in this version of the code).
• This test has a large number of threads (50) vs cpu cores (6), but that is probably not very relevant as we are not seeing high system CPU utilization and context switch rate, but will try running with less threads to verify.
• Cache size was 3 GB, and was full of dirty data; suspect larger cache size may exacerbate problem; will try.