CPython build options for out-of-the box performance

[alecsandrupatrascu]

BPO	26359
Nosy	@malemburg, @brettcannon, @gpshead, @pitrou, @scoder, @vstinner, @ned-deily, @bitdancer, @skrah, @zware, @zooba
PRs	[Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Dependencies	bpo-21122: CPython fails to build modules with LLVM LTO on Mac OS X
Files	cpython2_pgo_default-v01.patch cpython3_pgo_default-v02.patch cpython3_with_optimizations_v01.patch cpython2_with_optimizations_v01.patch cpython3_with_optimizations_v02.patch cpython2_with_optimizations_v02.patch cpython3_with_optimizations_v02-gps01.patch issue26359.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gpshead'
closed_at = <Date 2016-09-08.07:10:04.089>
created_at = <Date 2016-02-14.10:28:12.931>
labels = ['build', 'performance']
title = 'CPython build options for out-of-the box performance'
updated_at = <Date 2017-03-31.16:36:31.892>
user = 'https://bugs.python.org/alecsandrupatrascu'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:31.892>
actor = 'dstufft'
assignee = 'gregory.p.smith'
closed = True
closed_date = <Date 2016-09-08.07:10:04.089>
closer = 'gregory.p.smith'
components = ['Build']
creation = <Date 2016-02-14.10:28:12.931>
creator = 'alecsandru.patrascu'
dependencies = ['21122']
files = ['41918', '41919', '42576', '42871', '42872', '43142', '44406', '44412']
hgrepos = []
issue_num = 26359
keywords = ['patch']
message_count = 32.0
messages = ['260271', '263353', '263372', '263374', '263384', '263408', '263415', '263452', '263466', '264058', '265432', '265692', '265693', '265699', '266735', '267074', '267076', '273936', '274277', '274647', '274678', '274679', '274683', '274687', '274689', '274981', '275055', '275104', '275105', '275172', '281301', '288528']
nosy_count = 13.0
nosy_names = ['lemburg', 'brett.cannon', 'gregory.p.smith', 'pitrou', 'scoder', 'vstinner', 'ned.deily', 'r.david.murray', 'skrah', 'python-dev', 'zach.ware', 'steve.dower', 'alecsandru.patrascu']
pr_nums = ['552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue26359'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']

[alecsandrupatrascu]

Hello,

This is Alecsandru from the Dynamic Scripting Languages Optimization Team at Intel Corporation. I would like to submit a patch as a response to the discussion thread opened in Python-Dev (https://mail.python.org/pipermail/python-dev/2016-February/143215.html), regarding the way CPython is built, mainly the options that are available to the programmers. Analyzing the CPython ecosystem we can see that there are a lot of users that just download the sources and hit the commands "./configure", "make" and "make install" once and then continue using it with their Python scripts. One of the problems with this workflow it that the users do not benefit from the entire optimization features that are existing in the build system, such as PGO and LTO.

Therefore, I propose a workflow, like the following. Assume some work has to be done into the CPython interpreter, a developer can do the following steps:
A. Implementation and debugging phase.
1. The command "./configure PYDIST=debug" is ran once. It will enable the Py_DEBUG, -O0 and -g flags
2. The command "make" is ran once or multiple times

B. Testing the implementation from step A, in a pre-release environment
1. The command "./configure PYDIST=devel" is ran once. It will disable the Py_DEBUG flags and will enable the -O3 and -g flags, and it is just like the current implementation in CPython
2. The command "make" is ran once or multiple times

C. For any other CPython usage, for example distributing the interpreter, installing it inside an operating system, or just the majority of users who are not CPython developers and only want to compile it once and use it as-is:
1. The command "./configure" is ran once. Alternatively, the command "./configure PYDIST=release" can be used. It will disable all debugging functionality, enable the -O3 flag and will enable PGO and LTO.
2. The command "make" is ran once

Thank you,
Alecsandru

[vstinner]

Sorry, I don't understand this issue. I don't think that we need 3 flavors: debug, devel and release. We already have debug (--with-pydebug) and release, and IMHO debug is what developers should use.

I like the idea of using the best optimizers options *by default* for the release mode. In practice, I suggest to enable PGO *by default*.

[alecsandrupatrascu]

Hello Victor,

Indeed, the best outcome is to have PGO, LTO, etc enabled by default when running ./configure && make, for production level. I also feel that they should be on by default, if only developers would use the debug version.

Do you think that modifying the patches attached to this issue and enabling all optimizations by default could be considered acceptable by the Python community?

Thank you,
Alecsandru

[skrah]

Not acceptable, I'm afraid. See bpo-25702. I'm not sure why it is
considered so bothersome to type --with-pgo and --with-lto for
the rare case of a real production build.

[alecsandrupatrascu]

Maybe that end users are lazy and want to type just make and let things happen magically behind the scenes :-)

[zooba]

FWIW, I'm also against enabling it by default due to the extended build time. There are plenty of reasons to build Python with the non-debug ABI that don't require extended optimizations. Production builds are the exception I believe, not the rule.

[brettcannon]

What if we added a --with-optimizations flag to build --with-pgo, --with-lto, and avoid having to run make twice thanks to make/make profileopt? That way the default build is still quick and reasonable but gain a simple way to use the right flags and avoid having to remember to run make twice?

[gpshead]

--with-optimizations seems fine.

As does having the final thing the Makefile prints out when run from a configuration that did not specify any of --with-pgo, --with-lto, --with-pydebug, or --with-optimizations be to echo message reminding people to configure --with-optimizations when making a release build.

The default "./configure && make" target needs to remain optimized for CPython developer speed. Not release builds.

[alecsandrupatrascu]

That sounds like a good idea and plan, to have everything enabled with just one dedicated configure flag.

I can work on this and post the patches as soon as they are done.

Thank you

[alecsandrupatrascu]

I've added the --with-optimizations option to configure, for CPython3 only at this point. If it looks good I'll create a version also for CPython2.

[brettcannon]

The patch LGTM but I'm not a configure/make expert. Anyone else want to have a look?

Alecsandru, if no one takes a look within the next week then just assign the issue to me.

[alecsandrupatrascu]

I've attached a cleaner version for CPython 3 and one for CPython 2. The problem with CPython 2 is that Gregory did not yet merged the LTO on this branch (bpo-25702), but as soon as he does it, I'll post updated patches.

Regards,
Alecsandru

[alecsandrupatrascu]

Brett, I tried to add you in the "assigned to", but I do not have any rights to update those :(