Subject: [bug#47251] [core-updates] [patch] gnu: python: Enable optimizations.

From: Julien Lepiller <[email-masked]>
Date: Fri, 19 Mar 2021 00:16:22 +0100

Hi Guix!

This is the second patch I created in my exploration of our Python
package. Here, I noticed that our Python was very slow compared to
other distros and I tried to find which options they used. I found some
hints from Fedora. In this patch, I enable a few options and add a C/LD
flag to make python run faster.

I also attached a report of timing running the benchmark from
pyperformance on my Fedora machine. For comparison, I have also added
the results for Fedora's python3, which is somewhere in between.

I noticed that this increases the size of the python package by 20MB,
which is due entirely to --with-lto option, which also accounts for
half of the speedup. Overall, this python is almost twice as fast on
some benchmarks, and always faster on all of them. It's about 1.5 times
faster on average.

Strangely, the python package from Alpine is twice as small as this
package, and they use the --with-lto option. I wonder how they achieve
that.

Note that I modified python-2, as its flags are inherited by python-3
(and also the bootstrap python from commencement.scm).
>From c72e34aa0eb0db589557e047c5db0128273d5d12 Mon Sep 17 00:00:00 2001
From: Julien Lepiller <[email-masked]>
Date: Thu, 18 Mar 2021 23:41:40 +0100
Subject: [PATCH 2/2] gnu: python: Enable optimizations.

As a result, python execution time of scripts is decreased by 6 to 40%.

gnu/packages/python (python-2.7)[arguments]: Add configure and make flags to
optimize the resulting python.
---
 gnu/packages/python.scm | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/python.scm b/gnu/packages/python.scm
index da9859b11a..8de0ca343c 100644
--- a/gnu/packages/python.scm
+++ b/gnu/packages/python.scm
@@ -183,7 +183,10 @@
              "--with-system-expat"      ;for XML support
              "--with-system-ffi"        ;build ctypes
              "--with-ensurepip=install" ;install pip and setuptools
+             "--with-computed-gotos"    ;main interpreter loop optimization
+             "--with-lto"               ;increase size by 20MB, but 15% speedup
              "--enable-unicode=ucs4"
+             "--enable-optimizations"
 
              ;; Prevent the installed _sysconfigdata.py from retaining a reference
              ;; to coreutils.
@@ -197,8 +200,10 @@
                      "ac_cv_file__dev_ptmx=no"
                      "ac_cv_file__dev_ptc=no")
                    '())
+             "CFLAGS=-fno-semantic-interposition"
              (string-append "LDFLAGS=-Wl,-rpath="
-                            (assoc-ref %outputs "out") "/lib"))
+                            (assoc-ref %outputs "out") "/lib"
+                            " -fno-semantic-interposition"))
        ;; With no -j argument tests use all available cpus, so provide one.
        #:make-flags
        (list (string-append
-- 
2.30.0