[Bug libc/15943] New: localtime_r performance drop when set different timezone

[Bug libc/15943] New: localtime_r performance drop when set different timezone

[qd.feng@alcatel-lucent.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

            Bug ID: 15943
           Summary: localtime_r performance drop when set different
                    timezone
           Product: glibc
           Version: 2.12
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: qd.feng@alcatel-lucent.com
                CC: drepper.fsp at gmail dot com

There is one thread in our application frequently call the localtime_r. We
found the thread performance has 20% drop when change the timezone from the
America/New_york to Asia/Shanghai from the system(Redhat 6,). After profile, we
found it is the localtime_r cause the difference.

When set the timezone as America/New_york, the __tzfile_compute mainly call the
__tzstring. While when set the timezone as the Asia/Shanghai the
__tzfile_compute call the  __tzset_parse_tz which consume most of the CPU time. 

I also do an simple test on our HP G8 server. 

  1 #include <time.h>
  2 #include <stdio.h>
  3
  4  int main(void)
  5  {
  6         struct tm newtime;
  7            time_t ltime;
  8               char buf[50];
  9
 10                   for(int i=0;i<=1000000;i++)
 11                   {
 12                   ltime=time(&ltime);
 13
 14                   localtime_r(&ltime, &newtime);
 15                   }
 16  }

After compile and run command time ./a.out with the timezone as Asia/Shanghai
or 
America/New_York.
Asia/Shanghai 
real  0m1.838s
user  0m1.628s
sys   0m0.206s

America/New_York
real  0m0.608s
user  0m0.395s
sys   0m0.211s

There is no TZ env been set on both cases. I wonder what causes the performance
so difference, is it an designed behavior? 

Steven

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[Bug libc/15943] localtime_r performance drop when set different timezone

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> ---
How do you set the timezone?

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[Bug libc/15943] localtime_r performance drop when set different timezone

[qd.feng@alcatel-lucent.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

--- Comment #2 from Steven Feng <qd.feng@alcatel-lucent.com> ---
link the /etc/localtime to time zone under usr/share/zoneinfo/
e.g. 
ln -sf /usr/share/zoneinfo/America/New_York  /etc/localtime

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[Bug libc/15943] localtime_r performance drop when set different timezone

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug time/15943] localtime_r performance drop when set different timezone

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libc                        |time

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[Bug time/15943] localtime_r performance drop when set different timezone

[eggert at cs dot ucla.edu]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

eggert at cs dot ucla.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eggert at cs dot ucla.edu

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[Bug time/15943] localtime_r performance drop when set different timezone

[yann at droneaud dot fr]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

Yann Droneaud <yann at droneaud dot fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yann at droneaud dot fr

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[Bug time/15943] localtime_r performance drop when set different timezone

[eggert at cs dot ucla.edu]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

--- Comment #5 from eggert at cs dot ucla.edu ---
This glibc performance bug came up recently on the tz mailing list; see the
thread "[tz] localtime_r multiple times slower for Europe/Moscow timezone"
starting here:

https://mm.icann.org/pipermail/tz/2023-January/032522.html

That thread stems from the following Ubuntu bug report:

https://bugs.launchpad.net/ubuntu/+source/tzdata/+bug/868395

Guy Harris diagnosed the problem as glibc not properly caching the expansion of
the TZ string at the end of the TZif file. See:

https://mm.icann.org/pipermail/tz/2023-January/032529.html

This problem has grown in importance as many jurisdictions are now like Moscow,
as they formerly had daylight saving but now no longer do. So this performance
bug is more important now than it was years ago.

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[Bug time/15943] localtime_r performance drop when set different timezone

[gharris at sonic dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=15943

Guy Harris <gharris at sonic dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gharris at sonic dot net

--- Comment #6 from Guy Harris <gharris at sonic dot net> ---
Most if not all of China and India are also now no longer on DST, which is why
it happens with Asia/Shanghai.

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