Reduce lock contention in __tz_convert() [BZ #16145] (partial fix)

This patch is an "easy win" partial fix for BZ #16145, which notes
the heavy contention on tzset_lock when multiple threads are converting
times with localtime_r().

In __tz_convert(), the lock does not need to be held after
__tzfile_compute() / __tz_compute() have been called, so we can move the
unlock up.  At this point there is still significant work to be done in
__offtime(), so we see some improvement (in my testing with 8 cores
banging on localtime_r(), ~20% improvement in throughput).

diff --git a/ChangeLog b/ChangeLog
index e6db8ef..0d5c1f1 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2015-02-24  Kevin Easton  <kevin@guarana.org>
+
+       [BZ #16145] (partial fix)
+       * time/tzset.c (__tz_convert): Unlock tzset_lock earlier
+       to reduce lock contention.
+
 2015-02-24  Miroslav Lichvar  <mlichvar@redhat.com>
 
        * sysdeps/unix/sysv/linux/bits/timex.h: Update version.

diff --git a/time/tzset.c b/time/tzset.c
index 8bc7a2e..82324ca 100644 (file)
--- a/time/tzset.c
+++ b/time/tzset.c
@@ -644,6 +644,8 @@ __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
       leap_extra_secs = 0;
     }
 
+  __libc_lock_unlock (tzset_lock);
+
   if (tp)
     {
       if (! use_localtime)
@@ -659,8 +661,6 @@ __tz_convert (const time_t *timer, int use_localtime, struct tm *tp)
        tp = NULL;
     }
 
-  __libc_lock_unlock (tzset_lock);
-
   return tp;
 }