[tz] localtime_r multiple times slower for Europe/Moscow timezone

[Steffen Nurpmeso]

Steffen Nurpmeso wrote in
 <20230110235603.tclHE%steffen at sdaoden.eu>:
 |Benjamin Drung wrote in
 | <3f5601eaa696b06a12f3a578b3128b131ed3bbef.camel at canonical.com>:
 ||a Ubuntu user has been reporting in https://launchpad.net/bugs/868395
 ||that the Europe/Moscow timezone is multiple times slower than other
 ||timezones. Here is the example bug.c code:
 ||
 ||```
 ||#include <time.h>
 ||#include <stdio.h>
 ||
 ||int main() {
 ||  time_t t = time(0);
 ||  int i;
 ||  struct tm result;
 ||  for(i=0; i < 10000000; i++)
 ||    localtime_r(&t, &result);
 ||  puts(ctime(&t));
 ||  return 0;
 ||}
 ||```
 ...
 ||The result on my machine is that Etc/UTC, Europe/Berlin, and other
 ||timezones take around 250 to 400 ms, but Europe/Moscow takes 1200 ms.
 ||The result is the same when running in a Debian unstable, Ubuntu 22.04
 ||(jammy) and Ubuntu 23.04 (lunar) chroot.
 |
 |Wow, what performance.
 |
 |  #?0|kent:tmp$ for f in Etc/UTC Europe/Berlin Europe/Moscow; do time \
 |  TZ=$f ./zt; done
 |  real    0m0.520s
 |  user    0m0.515s
 |  sys     0m0.004s
 |  Wed Jan 11 00:51:58 2023
 |  real    0m7.202s
 |  user    0m7.180s
 |  sys     0m0.000s
 |  Wed Jan 11 02:52:05 2023
 |  real    0m2.076s
 |  user    0m2.071s
 |  sys     0m0.000s
 |
 ||Is that a bug? If yes, is that a bug in glibc?
 |
 |CRUX Linux, 2022g, 2.36-3, gcc 12.2.0.
 |
 |  #?0|kent:tmp$ zdump -v Europe/Berlin|wc -l
 |  2144
 |  #?0|kent:tmp$ zdump -v Europe/Moscow|wc -l
 |  166
 |  #?0|kent:tmp$ zdump -v Etc/UTC|wc -l
 |  6

..just to correct stupidity a little bit

  $ for f in Etc/UTC Europe/Berlin Europe/Moscow; do
    ef=$(echo $f | sed -E 's|/|\\/|')
    sed -E '/^Z '"$ef"'/,/^Z /p;d' /usr/share/zoneinfo/tzdata.zi
  done

comes to

  Z Etc/UTC 0 - UTC
  Z Etc/GMT 0 - GMT
  Z Europe/Berlin 0:53:28 - LMT 1893 Ap
  1 c CE%sT 1945 May 24 2
  1 So CE%sT 1946
  1 DE CE%sT 1980
  1 E CE%sT
  Z Europe/Gibraltar -0:21:24 - LMT 1880 Au 2
  Z Europe/Moscow 2:30:17 - LMT 1880
  2:30:17 - MMT 1916 Jul 3
  2:31:19 R %s 1919 Jul 1 0u
  3 R %s 1921 O
  3 R MSK/MSD 1922 O
  2 - EET 1930 Jun 21
  3 R MSK/MSD 1991 Mar 31 2s
  2 R EE%sT 1992 Ja 19 2s
  3 R MSK/MSD 2011 Mar 27 2s
  4 - MSK 2014 O 26 2s
  3 - MSK
  Z Europe/Simferopol 2:16:24 - LMT 1880

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)