[Python-Dev] Profile Guided Optimization active by-default

Brett Cannon brett at python.org
Sat Aug 22 18:25:06 CEST 2015

On Sat, Aug 22, 2015, 09:17 Guido van Rossum <guido at python.org> wrote:

How about we first add a new Makefile target that enables PGO, without
turning it on by default? Then later we can enable it by default.

I agree. Updating the Makefile so it's easier to use PGO is great, but we
should do a release with it as opt-in and go from there.

Also, I have my doubts about regrtest. How sure are we that it represents a
typical Python load? Tests are often using a different mix of operations
than production code.

That was also my question. You said that "it provides the best performance
improvement", but compared to what; what else was tried? And what
difference does it make to e.g. a Django app that is trained on their own
simulated workload compared to using regrtest? IOW is regrtest displaying
the best across-the-board performance because it stresses the largest swath
of Python and thus catches generic patterns in the code but individuals
could get better performance with a simulated workload?


On Sat, Aug 22, 2015 at 7:46 AM, Patrascu, Alecsandru <
alecsandru.patrascu at intel.com> wrote:

Hi All,

This is Alecsandru from Server Scripting Languages Optimization team at
Intel Corporation.

I would like to submit a request to turn-on Profile Guided Optimization or
PGO as the default build option for Python (both 2.7 and 3.6), given its
performance benefits on a wide variety of workloads and hardware.  For
instance, as shown from attached sample performance results from the Grand
Unified Python Benchmark, >20% speed up was observed.  In addition, we are
seeing 2-9% performance boost from OpenStack/Swift where more than 60% of
the codes are in Python 2.7. Our analysis indicates the performance gain
was mainly due to reduction of icache misses and CPU front-end stalls.

Attached is the Makefile patches that modify the all build target and adds
a new one called "disable-profile-opt". We built and tested this patch for
Python 2.7 and 3.6 on our Linux machines (CentOS 7/Ubuntu Server 14.04,
Intel Xeon Haswell/Broadwell with 18/8 cores).  We use "regrtest" suite for
training as it provides the best performance improvement.  Some of the test
programs in the suite may fail which leads to build fail.  One solution is
to disable the specific failed test using the "-x " flag (as shown in the

Steps to apply the patch:
1.  hg clone https://hg.python.org/cpython cpython
2.  cd cpython
3.  hg update 2.7 (needed for 2.7 only)
4.  Copy *.patch to the current directory
5.  patch < python2.7-pgo.patch (or patch < python3.6-pgo.patch)
6.  ./configure
7.  make

To disable PGO
7b. make disable-profile-opt

In the following, please find our sample performance results from latest
XEON machine, XEON Broadwell EP.
Hardware (HW):      Intel XEON (Broadwell) 8 Cores

BIOS settings:      Intel Turbo Boost Technology: false
                    Hyper-Threading: false

Operating System:   Ubuntu 14.04.3 LTS trusty

OS configuration:   CPU freq set at fixed: 2.6GHz by
                        echo 2600000 >
                        echo 2600000 >
                    Address Space Layout Randomization (ASLR) disabled (to
reduce run to run variation) by
                        echo 0 > /proc/sys/kernel/randomize_va_space

GCC version:        gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04)

Benchmark:          Grand Unified Python Benchmark (GUPB)
                    GUPB Source: https://hg.python.org/benchmarks/

Python2.7 results:
    Python source: hg clone https://hg.python.org/cpython cpython
    Python Source: hg update 2.7
    hg id: 0511b1165bb6 (2.7)
    hg id -r 'ancestors(.) and tag()': 15c95b7d81dc (2.7) v2.7.10
    hg --debug id -i: 0511b1165bb6cf40ada0768a7efc7ba89316f6a5

        Benchmarks          Speedup(%)
        simple_logging      20
        raytrace            20
        silent_logging      19
        richards            19
        chaos               16
        formatted_logging   16
        json_dump           15
        hexiom2             13
        pidigits            12
        slowunpickle        12
        django_v2           12
        unpack_sequence     11
        float               11
        mako                11
        slowpickle          11
        fastpickle          11
        django              11
        go                  10
        json_dump_v2        10
        pathlib             10
        regex_compile       10
        pybench             9.9
        etree_process       9
        regex_v8            8
        bzr_startup         8
        2to3                8
        slowspitfire        8
        telco               8
        pickle_list         8
        fannkuch            8
        etree_iterparse     8
        nqueens             8
        mako_v2             8
        etree_generate      8
        call_method_slots   7
        html5lib_warmup     7
        html5lib            7
        nbody               7
        spectral_norm       7
        spambayes           7
        fastunpickle        6
        meteor_contest      6
        chameleon           6
        rietveld            6
        tornado_http        5
        unpickle_list       5
        pickle_dict         4
        regex_effbot        3
        normal_startup      3
        startup_nosite      3
        etree_parse         2
        call_method_unknown 2
        call_simple         1
        json_load           1
        call_method         1

Python3.6 results
    Python source: hg clone https://hg.python.org/cpython cpython
    hg id: 96d016f78726 tip
    hg id -r 'ancestors(.) and tag()': 1a58b1227501 (3.5) v3.5.0rc1
    hg --debug id -i: 96d016f78726afbf66d396f084b291ea43792af1

        Benchmark           Speedup(%)
        fastunpickle        22.94
        fastpickle          21.67
        json_load           17.64
        simple_logging      17.49
        meteor_contest      16.67
        formatted_logging   15.33
        etree_process       14.61
        raytrace            13.57
        etree_generate      13.56
        chaos               12.09
        hexiom2             12
        nbody               11.88
        json_dump_v2        11.24
        richards            11.02
        nqueens             10.96
        fannkuch            10.79
        go                  10.77
        float               10.26
        regex_compile       9.8
        silent_logging      9.63
        pidigits            9.58
        etree_iterparse     9.48
        2to3                8.44
        regex_v8            8.09
        regex_effbot        7.88
        call_simple         7.63
        tornado_http        7.38
        etree_parse         4.92
        spectral_norm       4.72
        normal_startup      4.39
        telco               3.88
        startup_nosite      3.7
        call_method         3.63
        unpack_sequence     3.6
        call_method_slots   2.91
        call_method_unknown 2.59
        iterative_count     0.45
        threaded_count      -2.79

Thank you,

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--Guido van Rossum (python.org/~guido)

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