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).

1 files changed, 6 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index e6db8ef0ba..0d5c1f1fd2 100644
--- 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.