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List:       apache-httpd-dev
Subject:    Re: svn commit: r1599625 - /httpd/httpd/trunk/server/mpm/event/event.c
From:       Christophe JAILLET <christophe.jaillet () wanadoo ! fr>
Date:       2015-09-29 5:17:07
Message-ID: 560A1ED3.9050208 () wanadoo ! fr
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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, jim@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
> 
> 
> 


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    <div class="moz-cite-prefix">Hi,<br>
      <br>
      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.<br>
      <br>
      I looked at r1599625 + r1599641, which set the TZ environment
      variable, if unset, in order to have a small performance boost.<br>
      <br>
      <br>
      First, I've not been able to reproduce the 2% performance boost
      described in the patch.<br>
      My system is Ubuntu 15.04 and $TZ is apparently empty.<br>
      <br>
      <br>
      Second, I don't think that this patch should be backported as-is
      because it may change the timestamp in the log file.<br>
      <br>
      <br>
      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 <i>localtime</i> file.<br>
      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.<br>
      <br>
      <br>
      However,<br>
        - I don't know if this is portable<br>
        - I'm unsure about how daylight saving time will be handled<br>
      <br>
      <br>
      Any thought ?<br>
      <br>
      Best regards,<br>
      CJ<br>
      <br>
      <br>
      <br>
      [1]: <a class="moz-txt-link-freetext" \
href="http://linux.die.net/man/3/tzset">http://linux.die.net/man/3/tzset</a><br>  \
<br>  Le 03/06/2014 17:49, <a class="moz-txt-link-abbreviated"
        href="mailto:jim@apache.org">jim@apache.org</a> a écrit :<br>
    </div>
    <blockquote cite="mid:20140603154925.B0707238896F@eris.apache.org"
      type="cite">
      <pre wrap="">Author: jim
Date: Tue Jun  3 15:49:25 2014
New Revision: 1599625

URL: <a class="moz-txt-link-freetext" \
href="http://svn.apache.org/r1599625">http://svn.apache.org/r1599625</a> 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: <a class="moz-txt-link-freetext" \
href="http://svn.apache.org/viewvc/httpd/httpd/trunk/server/mpm/event/event.c?rev=1599 \
625&amp;r1=1599624&amp;r2=1599625&amp;view=diff">http://svn.apache.org/viewvc/httpd/ht \
tpd/trunk/server/mpm/event/event.c?rev=1599625&amp;r1=1599624&amp;r2=1599625&amp;view=diff</a>
 ==============================================================================
--- 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 &lt;stdlib.h&gt;
@@ -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:
+     *   <a class="moz-txt-link-rfc2396E" \
href="http://www.gnu.org/s/hello/manual/libc/TZ-Variable.html">&lt;http://www.gnu.org/s/hello/manual/libc/TZ-Variable.html&gt;</a>
 +     */
+    char *v = NULL;
+
+    if (apr_env_get(&amp;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



</pre>
    </blockquote>
    <br>
  </body>
</html>



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