[issue22003] BytesIO copy-on-write

[David Wilson]

David Wilson added the comment:

Newest patch incorporates Antoine's review comments. The final benchmark results are below. Just curious, what causes e.g. telco to differ up to 7% between runs? That's really huge

Report on Linux k2 3.14-1-amd64 #1 SMP Debian 3.14.9-1 (2014-06-30) x86_64
Total CPU cores: 4

### call_method_slots ###
Min: 0.329869 -> 0.340487: 1.03x slower
Avg: 0.330512 -> 0.341786: 1.03x slower
Significant (t=-216.69)
Stddev: 0.00067 -> 0.00060: 1.1111x smaller

### call_method_unknown ###
Min: 0.351167 -> 0.343961: 1.02x faster
Avg: 0.351731 -> 0.344580: 1.02x faster
Significant (t=238.89)
Stddev: 0.00033 -> 0.00040: 1.2271x larger

### call_simple ###
Min: 0.257487 -> 0.277366: 1.08x slower
Avg: 0.257942 -> 0.277809: 1.08x slower
Significant (t=-845.64)
Stddev: 0.00029 -> 0.00029: 1.0126x smaller

### etree_generate ###
Min: 0.377985 -> 0.365952: 1.03x faster
Avg: 0.381797 -> 0.369452: 1.03x faster
Significant (t=31.15)
Stddev: 0.00314 -> 0.00241: 1.3017x smaller

### etree_iterparse ###
Min: 0.545668 -> 0.565437: 1.04x slower
Avg: 0.554188 -> 0.576807: 1.04x slower
Significant (t=-17.00)
Stddev: 0.00925 -> 0.00956: 1.0340x larger

### etree_process ###
Min: 0.294158 -> 0.286617: 1.03x faster
Avg: 0.296354 -> 0.288877: 1.03x faster
Significant (t=36.22)
Stddev: 0.00149 -> 0.00143: 1.0435x smaller

### fastpickle ###
Min: 0.458961 -> 0.475828: 1.04x slower
Avg: 0.460226 -> 0.481228: 1.05x slower
Significant (t=-109.38)
Stddev: 0.00082 -> 0.00173: 2.1051x larger

### nqueens ###
Min: 0.305883 -> 0.295858: 1.03x faster
Avg: 0.308085 -> 0.297755: 1.03x faster
Significant (t=90.22)
Stddev: 0.00077 -> 0.00085: 1.0942x larger

### silent_logging ###
Min: 0.074152 -> 0.075818: 1.02x slower
Avg: 0.074345 -> 0.076005: 1.02x slower
Significant (t=-96.29)
Stddev: 0.00013 -> 0.00012: 1.0975x smaller

### spectral_norm ###
Min: 0.355738 -> 0.364419: 1.02x slower
Avg: 0.356691 -> 0.365764: 1.03x slower
Significant (t=-126.23)
Stddev: 0.00054 -> 0.00047: 1.1533x smaller

### telco ###
Min: 0.012152 -> 0.013038: 1.07x slower
Avg: 0.012264 -> 0.013157: 1.07x slower
Significant (t=-83.98)
Stddev: 0.00008 -> 0.00007: 1.0653x smaller

The following not significant results are hidden, use -v to show them:
2to3, call_method, chaos, django_v2, etree_parse, fannkuch, fastunpickle, float, formatted_logging, go, hexiom2, iterative_count, json_dump, json_dump_v2, json_load, mako, mako_v2, meteor_contest, nbody, normal_startup, pathlib, pickle_dict, pickle_list, pidigits, raytrace, regex_compile, regex_effbot, regex_v8, richards, simple_logging, startup_nosite, threaded_count, tornado_http, unpack_sequence, unpickle_list.

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Added file: http://bugs.python.org/file36137/cow6.patch

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<http://bugs.python.org/issue22003>
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