GNU bug report logs - #38322
GCC optimize levels makes huge impact on performance

Previous Next

Full log

View this message in rfc822 format

From: Balázs Vinarz <vinibali1 <at> gmail.com>
To: 38322 <at> debbugs.gnu.org
Subject: bug#38322: GCC optimize levels makes huge impact on performance
Date: Fri, 22 Nov 2019 18:00:29 +0200

Hello there!

Today I was working on two bigger, plain text, csv-like database files
(file1: ~175k lines and 15MB, file2: ~ 168k lines and 14MB). I just
searched for lines, using grep -f $file2 $file1. I was so surprised
when I realized the search was running for minutes already without a
single line at the standard output. I decided to have a try with
custom compiled binaries, because in my mind the size optimized
binaries are the fastest.
In the end grep (3.1) was running for:
- 4m50s if I used the one was coming from Ubuntu,
- 4m29s in case of custom recompiled with GCC7.4 and CFLAGS="O2" and
- 3m17s in case of custom recompiled with GCC7.4 and CFLAGS="Os".
I repeated the runs multiple times, I would say it's accurate. The
files were located on tmpfs.
Binary sizes are: 215K for Ubuntu, 184K for O2 and 150K for Os.
CPU: Intel I5-8350U
OS: Ubuntu 18.04.3 LTS
Would you mind change the default optimize level on the make
configuration? Did somebody ever measured the benefits using different
GCC optimalization levels?
I know that this is a special use case, but the improvement is huge.
I'm looking forward for your feedback.

Best regards

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.