Re: svn commit: r1599625 - /httpd/httpd/trunk/server/mpm/event/event.c

[Christophe JAILLET]

Hi,

now that SO_REUSEPORT has landed on 2.4.x, it is easier to try to synch 
2.4.x and trunk a bit more.

I looked at r1599625 + r1599641, which set the TZ environment variable, 
if unset, in order to have a small performance boost.


First, I've not been able to reproduce the 2% performance boost 
described in the patch.
My system is Ubuntu 15.04 and $TZ is apparently empty.


Second, I don't think that this patch should be backported as-is because 
it may change the timestamp in the log file.


However, I was wondering if we could call tzset() and use tzname[0] or 
tzname[1] instead of the hard coded "UTC+0". According to [1], tzset() 
first looks at TZ, but, if not set, then at the /localtime/ file.
This way, we could define TZ if it can be a performance boost in some 
cases and avoid the change of behavior on existing systems.


However,
  - I don't know if this is portable
  - I'm unsure about how daylight saving time will be handled


Any thought ?

Best regards,
CJ



[1]: http://linux.die.net/man/3/tzset

Le 03/06/2014 17:49, j...@apache.org a écrit :
Author: jim
Date: Tue Jun  3 15:49:25 2014
New Revision: 1599625

URL:http://svn.apache.org/r1599625
Log:
fold in performance hack from eventopt

Modified:
     httpd/httpd/trunk/server/mpm/event/event.c

Modified: httpd/httpd/trunk/server/mpm/event/event.c
URL:http://svn.apache.org/viewvc/httpd/httpd/trunk/server/mpm/event/event.c?rev=1599625&r1=1599624&r2=1599625&view=diff
==============================================================================
--- httpd/httpd/trunk/server/mpm/event/event.c (original)
+++ httpd/httpd/trunk/server/mpm/event/event.c Tue Jun  3 15:49:25 2014
@@ -57,6 +57,8 @@
  #include "apr_atomic.h"
  #define APR_WANT_STRFUNC
  #include "apr_want.h"
+#include "apr_env.h"
+
  #include "apr_version.h"
  
  #include <stdlib.h>
@@ -2418,6 +2420,25 @@ static void join_start_thread(apr_thread
      }
  }
  
+static void force_set_tz(apr_pool_t *p) {
+    /* If the TZ variable is unset, many operationg systems,
+     * such as Linux, will at runtime read from /etc/localtime
+     * and call fstat on it.
+     *
+     * By forcing the time zone to UTC if it is unset, we gain
+     * about 2% in raw requests/second (since we format log files
+     * in the local time, if present)
+     *
+     * For more info, see:
+     *<http://www.gnu.org/s/hello/manual/libc/TZ-Variable.html>
+     */
+    char *v = NULL;
+
+    if (apr_env_get(&v, "TZ", p) != APR_SUCCESS) {
+        apr_env_set("TZ", "UTC+0", p);
+    }
+}
+
  static void child_main(int child_num_arg)
  {
      apr_thread_t **threads;
@@ -3566,6 +3587,7 @@ static void event_hooks(apr_pool_t * p)
       */
      static const char *const aszSucc[] = { "core.c", NULL };
      one_process = 0;
+    force_set_tz(p);
  
      ap_hook_open_logs(event_open_logs, NULL, aszSucc, APR_HOOK_REALLY_FIRST);
      /* we need to set the MPM state before other pre-config hooks use MPM 
query