I ran perf to use calibration and there is no difference in stability
compared to the unpatched version.

With patch:

python perf.py -b json_dump_v2 -v --csv=out1.csv --affinity=2 ../cpython/python ../cpython/python
INFO:root:Automatically selected timer: perf_counter
[1/1] json_dump_v2...
Calibrating
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 1 -l 1 --timer perf_counter`
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 1 -l 2 --timer perf_counter`
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 1 -l 4 --timer perf_counter`
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 1 -l 8 --timer perf_counter`
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 1 -l 16 --timer perf_counter`
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 1 -l 32 --timer perf_counter`
Calibrating => num_runs=10, num_loops=32 (0.50 sec < 0.87 sec)
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 10 -l 32 --timer perf_counter`
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 10 -l 32 --timer perf_counter`

Report on Linux centos 3.10.0-229.7.2.el7.x86_64 #1 SMP Tue Jun 23 22:06:11 UTC 2015 x86_64 x86_64
Total CPU cores: 18

### json_dump_v2 ###
Min: 0.877497 -> 0.886482: 1.01x slower   <----------
Avg: 0.878150 -> 0.888351: 1.01x slower
Not significant
Stddev: 0.00054 -> 0.00106: 1.9481x larger


Without patch:

python perf.py -b json_dump_v2 -v --csv=out1.csv --affinity=2 ../cpython/python ../cpython/python
INFO:root:Automatically selected timer: perf_counter
[1/1] json_dump_v2...
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 50 --timer perf_counter`
INFO:root:Running `taskset --cpu-list 2 ../cpython/python performance/bm_json_v2.py -n 50 --timer perf_counter`

Report on Linux centos 3.10.0-229.7.2.el7.x86_64 #1 SMP Tue Jun 23 22:06:11 UTC 2015 x86_64 x86_64
Total CPU cores: 18

### json_dump_v2 ###
Min: 2.755514 -> 2.764131: 1.00x slower     <---------- (almost) same as above
Avg: 2.766546 -> 2.775587: 1.00x slower
Not significant
Stddev: 0.00538 -> 0.00382: 1.4069x smaller