[issue17781] optimize compilation options

[Zachary Ware]

Zachary Ware  added the comment:

After 2.5 years without response, I think the answer is probably "no" :)

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[issue17781] optimize compilation options

[Zachary Ware]

Zachary Ware added the comment:

PGO is available as `make profile-opt`, LTO has a patch in issue25702.  Are 
there any other interesting options worth investigating?

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[issue17781] optimize compilation options

[R. David Murray]

Changes by R. David Murray :


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[issue17781] optimize compilation options

[R. David Murray]

Changes by R. David Murray :


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[issue17781] optimize compilation options

[Alecsandru Patrascu]

Alecsandru Patrascu added the comment:

Hi, I added a dedicated issue just for LTO only when using GCC and CLANG 
(http://bugs.python.org/issue25702), that works well with PGO also.

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[issue17781] optimize compilation options

[Terry J. Reedy]

Terry J. Reedy added the comment:

#24915 is about adding pgo and has a slew of patches.

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[issue17781] optimize compilation options

[Matthias Klose]

Matthias Klose added the comment:

On 22.09.2015 12:31, Antoine Pitrou wrote:
> Also note LTO can make compilation times much longer (it's the linking step 
> actually, which can take minutes).

use -flto=jobserver

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[issue17781] optimize compilation options

[STINNER Victor]

STINNER Victor added the comment:

> For the record, the gain for LTO+PGO (with "-flto -O3") over PGO alone seems 
> to be between 0% and 10% for most benchmarks.

Hum, does it make sense to enable LTO without PGO?

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[issue17781] optimize compilation options

[Antoine Pitrou]

Antoine Pitrou added the comment:

Note this patch is likely wrong, as it doesn't add the optimization options to 
the linker invocation. According to the gcc does, To use the link-time 
optimizer, -flto and optimization options should be specified at compile time 
and during the final link.

So probably $OPT should be added to $PY_LDFLAGS.

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[issue17781] optimize compilation options

[Antoine Pitrou]

Antoine Pitrou added the comment:

You can test for yourself by passing `CFLAGS=-flto -O3 LDFLAGS=-flto -O3` 
to ./configure (using gcc).

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[issue17781] optimize compilation options

[Antoine Pitrou]

Antoine Pitrou added the comment:

For the record, the gain for LTO+PGO (with -flto -O3) over PGO alone seems to 
be between 0% and 10% for most benchmarks.

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[issue17781] optimize compilation options

[Raymond Hettinger]

Raymond Hettinger added the comment:

I would like the see LTO enabled.  The intermodule calls to code in abstract.c 
would become less expensive.

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[issue17781] optimize compilation options

[Antoine Pitrou]

Antoine Pitrou added the comment:

LTO (Link-Time Optimization) is not the same as PGO, though I guess it can take 
advantage of PGO for its heuristics.

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[issue17781] optimize compilation options

[Stefan Behnel]

Stefan Behnel added the comment:

Issue 24915 suggests PGO and comes with an actual patch. I suggest rejecting 
this ticket as too broad.

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[issue17781] optimize compilation options

[Stefan Krah]

Changes by Stefan Krah stefan-use...@bytereef.org:


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[issue17781] optimize compilation options

[Stefan Krah]

Changes by Stefan Krah stefan-use...@bytereef.org:


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[issue17781] optimize compilation options

[Christian Heimes]

Christian Heimes added the comment:

Here is a patch for -flto. You need to run autoconf to re-generate configure, 
too.

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Added file: http://bugs.python.org/file29920/lto_flag.patch

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[issue17781] optimize compilation options

[Matthias Klose]

Matthias Klose added the comment:

the proposed patch is wrong. when linking with -flto, you should pass all the 
relevant CFLAGS to the linker as well. Also pass -fuse-linker-plugin.

and this should be an opt-in, not the default. Depending on the architecture 
and the compiler version, -flto is not as stable as you want it to be.

and last, this ends up as the default for building third party extensions too, 
which again, I think should be an opt-in.

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[issue17781] optimize compilation options

[Antoine Pitrou]

New submission from Antoine Pitrou:

Ubuntu's system Python 3.3 shows consistently better performance than a vanilla 
Python 3.3: around 10-15% faster in general (see attached benchmark numbers).

If this can be attributed to different compilation options, it would be nice to 
backport those options to our standard build config.

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components: Build
files: perflog.txt
messages: 187192
nosy: barry, doko, pitrou
priority: low
severity: normal
status: open
title: optimize compilation options
type: performance
versions: Python 3.4
Added file: http://bugs.python.org/file29907/perflog.txt

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[issue17781] optimize compilation options

[Matthias Klose]

Matthias Klose added the comment:

most of that can be attributed to the pgo build, which is upstream for a long 
time. the second thing to do is to build with lto, and see what speedups you 
get in addition. and it certainly helps to build the interpreter statically 
(without --enable-shared).

but thanks to confirming my own experience ;)

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