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authorIngo Molnar <mingo@elte.hu>2007-07-15 23:41:18 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-16 09:05:48 -0700
commit4e44f3497d41db4c3b9051c61410dee8ae4fb49c (patch)
tree8c54919894c8f6ac629c6c28cee8fb504721d652 /kernel/time.c
parentf482394ccbca7234d29cc146d4a2b94f976ce5a1 (diff)
downloadlinux-4e44f3497d41db4c3b9051c61410dee8ae4fb49c.tar.bz2
sys_time() speedup
Improve performance of sys_time(). sys_time() returns time in seconds, but it does so by calling do_gettimeofday() and then returning the tv_sec portion of the GTOD time. But the data structure "xtime", which is updated by every timer/scheduler tick, already offers HZ granularity time. The patch improves the sysbench OLTP macrobenchmark significantly: 2.6.22-rc6: #threads 1: transactions: 3733 (373.21 per sec.) 2: transactions: 6676 (667.46 per sec.) 3: transactions: 6957 (695.50 per sec.) 4: transactions: 7055 (705.48 per sec.) 5: transactions: 6596 (659.33 per sec.) 2.6.22-rc6 + sys_time.patch: 1: transactions: 4005 (400.47 per sec.) 2: transactions: 7379 (737.77 per sec.) 3: transactions: 7347 (734.49 per sec.) 4: transactions: 7468 (746.65 per sec.) 5: transactions: 7428 (742.47 per sec.) Mixed API uses of gettimeofday() and time() are guaranteed to be coherent via the use of a at-most-once-per-second slowpath that updates xtime. [akpm@linux-foundation.org: build fixes] Signed-off-by: Ingo Molnar <mingo@elte.hu> Cc: John Stultz <johnstul@us.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Roman Zippel <zippel@linux-m68k.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/time.c')
-rw-r--r--kernel/time.c32
1 files changed, 24 insertions, 8 deletions
diff --git a/kernel/time.c b/kernel/time.c
index f04791f69408..ffe19149d770 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -57,14 +57,17 @@ EXPORT_SYMBOL(sys_tz);
*/
asmlinkage long sys_time(time_t __user * tloc)
{
- time_t i;
- struct timeval tv;
+ /*
+ * We read xtime.tv_sec atomically - it's updated
+ * atomically by update_wall_time(), so no need to
+ * even read-lock the xtime seqlock:
+ */
+ time_t i = xtime.tv_sec;
- do_gettimeofday(&tv);
- i = tv.tv_sec;
+ smp_rmb(); /* sys_time() results are coherent */
if (tloc) {
- if (put_user(i,tloc))
+ if (put_user(i, tloc))
i = -EFAULT;
}
return i;
@@ -373,12 +376,25 @@ void do_gettimeofday (struct timeval *tv)
tv->tv_sec = sec;
tv->tv_usec = usec;
-}
+ /*
+ * Make sure xtime.tv_sec [returned by sys_time()] always
+ * follows the gettimeofday() result precisely. This
+ * condition is extremely unlikely, it can hit at most
+ * once per second:
+ */
+ if (unlikely(xtime.tv_sec != tv->tv_sec)) {
+ unsigned long flags;
+
+ write_seqlock_irqsave(&xtime_lock, flags);
+ update_wall_time();
+ write_sequnlock_irqrestore(&xtime_lock, flags);
+ }
+}
EXPORT_SYMBOL(do_gettimeofday);
+#else /* CONFIG_TIME_INTERPOLATION */
-#else
#ifndef CONFIG_GENERIC_TIME
/*
* Simulate gettimeofday using do_gettimeofday which only allows a timeval
@@ -394,7 +410,7 @@ void getnstimeofday(struct timespec *tv)
}
EXPORT_SYMBOL_GPL(getnstimeofday);
#endif
-#endif
+#endif /* CONFIG_TIME_INTERPOLATION */
/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
* Assumes input in normal date format, i.e. 1980-12-31 23:59:59