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Victor Stinner - Optimizations which made Pytho...

Victor Stinner - Optimizations which made Python 3.6 faster than Python 3.5

Various optimizations made Python 3.6 faster than Python 3.5. Let's see in detail what was done and how.

Python 3.6 is faster than any other Python version on many benchmarks. We will see results of the Python benchmark suite on Python 2.7, 3.5 and 3.6.

The bytecode format and instructions to call functions were redesign to run bytecode faster.

A new C calling convention, called "fast call", was introduced to avoid temporary tuple and dict. The way Python parses arguments was also optimized using a new internal cache.

Operations on bytes and encodes like UTF-8 were optimized a lot thanks to a new API to create bytes objects. The API allows very efficient optimizations and reduces memory reallocations.

Some parts of asyncio were rewritten in C to speedup code up to 25%. The PyMem_Malloc() function now also uses the fast pymalloc allocator also giving tiny speedup for free.

Finally, we will see optimization projects for Python 3.7: use fast calls in more cases, speed up method calls, a cache on opcodes, a cache on global variables.

https://us.pycon.org/2017/schedule/presentation/487/

PyCon 2017

May 21, 2017
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Transcript

  1. (1) Benchmarks (2) Benchmarks results (3) Python 3.5 optimizations (4)

    Python 3.6 optimizations (5) Python 3.7 optimizations Agenda
  2. March 2016, no developer trusted the Python benchmark suite Many

    benchmarks were unstable It wasn’t possible to decide if an optimization makes CPython faster or not... Unstable benchmarks
  3. Calibrate the number of loops Spawn 20 processes sequentially, 3

    values per process, total: 60 values Compute average (mean) and standard deviation New perf module
  4. Benchmarks rewritten using perf: new project performance on GitHub http://speed.python.org

    now runs performance CPython is now compiled with Link Time Optimization (LTO) and Profile Guided Optimization (PGO) performance project
  5. sudo python3 -m perf system tune Use fixed CPU frequency

    Disable Intel Turbo Boost If CPU isolation is enabled, Linux kernel options isolcpus and rcu_nocbs, use CPU pinning CPU isolation helps a lot to reduce operation system jitter Linux and CPUs
  6. telco: 3.6 vs 2.7 Python 3.6 is 40x faster than

    Python 2.7 (decimal module rewritten in C by Stefan Krah in Python 3.3)
  7. Matt Joiner, Alexey Kachayev and Serhiy Storchaka reimplemented functools.lru_cache() in

    C sympy: 20% faster scimark_lu: 5% faster Tricky C code, hard to get it right: 3 years ½ to close the bpo-14373 lru_cache()
  8. Eric Snow reimplemented collections.OrderedDict in C html5lib: 20% faster Reuse

    C implementation of dict Again, tricky C code: 2 years ½ to close the bpo-16991 OrderedDict
  9. Victor Stinner changed PyMem_Malloc() to use Python fast memory allocator

    Many benchmarks: 5% - 22% faster Check if the GIL is held in debug hooks Only numy misused the API (fixed) PYTHONMALLOC=debug now available in release builds to detect memory corruptions, bpo-26249 PyMem_Malloc()
  10. Serhiy Storchaka optimized ElementTree.iterparse() 2x faster Follow-up of Brett Canon’s

    Pycon Canada 2015 keynote :-) bpo-25638 ElementTree parse
  11. Brett Canon modified the Profile Guided Optimization (PGO) The Python

    test suite is now used, rather than pidigits, to guide the compiler Many benchmarks: 5% – 27% faster bpo-24915 PGO uses tests
  12. Demur Rumed and Serhiy Storchaka modified the bytecode to always

    use 2 bytes opcodes Before: 1 (no arg) or 3 bytes (with arg) Removed an if from ceval.c hotcode for better CPU branch prediction: if (HAS_ARG(opcode)) oparg = NEXTARG(); bpo-26647 Wordcode
  13. Victor Stinner wrote a new C API to avoid the

    creation of temporary tuples to pass function arguments Many microbenchmarks: 12% – 50% faster obj[0], getattr(obj, "attr"), {1: 2}.get(1), list.count(0), str.replace("a","b"), … Avoid 20 ns per modified function call FASTCALL
  14. Victor Stinner optimized ASCII and UTF-8 codecs for ignore, replace,

    surrogateescape and surrogatepass error handlers UTF-8: decoder 15x faster, encoder 75x faster ASCII: decoder 60x faster, encoder 3x faster Unicode codecs
  15. PEP 461 added back bytes % args to Python 3.5

    Victor Stinner wrote a new _PyBytesWriter API to optimize functions creating bytes and bytearray strings bytes % args: 2x faster bytes.fromhex(): 3x faster bytes % args
  16. Serhiy Storchaka optimized glob.glob(), glob.iglob() and pathlib globbing using os.scandir()

    (new in Python 3.5) glob: 3x - 6x faster Pathlib glob: 1.5x - 4x faster Avoid one stat() per directory entry bpo-25596, bpo-26032 Globbing
  17. Yury Selivanov and Naoki INADA reimplemented asyncio Future and Task

    classes in C Asyncio programs: 30% faster bpo-26081, bpo-28544 asyncio
  18. Yury Selivanov and Naoki INADA added LOAD_METHOD and CALL_METHOD opcodes

    Methods calls: 10% - 20% faster Idea coming from PyPy, bpo-26110 Method calls