| Subject: | strptime significantly slower in 1.30 and 1.31 |
| Date: | Wed, 23 Nov 2016 19:08:41 +0000 |
| To: | bug-Time-Piece [...] rt.cpan.org |
| From: | Brian Bailey <bbailey1024 [...] gmail.com> |
The _mktime function was modified in Time::Piece 1.29_05 to include a call
to Time::Local::timegm.
https://github.com/rjbs/Time-Piece/commit/e6156357c8a151287a097d3be93b3f060dc2ed36
This results in a significant slowdown in strptime. The following benchmark
demonstrates this.
#!/usr/bin/perl
use Time::Piece;
use Benchmark qw(:all);
my $time = "2016-11-21 00:00:00 -0000";
timethese(-20, {
'TP' => sub { my $tp = Time::Piece->strptime($time, "%Y-%m-%d %H:%M:%S
%z"); }
});
Time::Piece 1.29
Benchmark: running TP for at least 20 CPU seconds...
TP: 21 wallclock secs (20.95 usr + 0.00 sys = 20.95 CPU) @
126935.70/s (n=2659303)
Time::Piece 1.31
Benchmark: running TP for at least 20 CPU seconds...
TP: 22 wallclock secs (20.84 usr + 0.00 sys = 20.84 CPU) @
65663.44/s (n=1368426)
The following NYTProf results identify Time::Local::timegm as the culprit
(taken from our production environment).
Time::Piece 1.29
# spent 7.51ms within Time::Piece::_mktime which was called 457 times, avg
16µs/call:
# 457 times (7.51ms+0s) by Time::Piece::strptime at line 471, avg 16µs/call
Time::Piece 1.31
# spent 41.5ms (15.7+25.7) within Time::Piece::_mktime which was called 500
times, avg 83µs/call:
# 500 times (15.7ms+25.7ms) by Time::Piece::strptime at line 483, avg
83µs/call
# spent 25.7ms making 500 calls to Time::Local::timegm, avg 51µs/call
The functionality added in the above commit does not seem worth the
overhead.
perl -v
This is perl 5, version 22, subversion 2 (v5.22.2) built for x86_64-linux
(with 30 registered patches, see perl -V for more detail)
uname -a
Linux host 4.4.26-gentoo #1 SMP Thu Nov 3 03:10:42 UTC 2016 x86_64 AMD
Opteron(tm) Processor 6378 AuthenticAMD GNU/Linux