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

["qd.feng@alcatel-lucent.com" <sourceware-bugzilla@sourceware.org>]

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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