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

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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, [hidden email] 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




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

Eric Covener
On Tue, Sep 29, 2015 at 1:17 AM, Christophe JAILLET
<[hidden email]> wrote:

>
> 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


A better guess would be nice.  When the runtime doesn't match the test
suite, some tests (ssl/varlookup.t) can fail when the timezone is
behind/ahead on day of the week from UTC.