Subject: time: introduce xtime_seconds
From: Ingo Molnar <[email protected]>
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 by 4-5% on an AMD
dual-core system:
v2.6.23:
#threads
1: transactions: 4073 (407.23 per sec.)
2: transactions: 8530 (852.81 per sec.)
3: transactions: 8321 (831.88 per sec.)
4: transactions: 8407 (840.58 per sec.)
5: transactions: 8070 (806.74 per sec.)
v2.6.23 + sys_time-speedup.patch:
1: transactions: 4281 (428.09 per sec.)
2: transactions: 8910 (890.85 per sec.)
3: transactions: 8659 (865.79 per sec.)
4: transactions: 8676 (867.34 per sec.)
5: transactions: 8532 (852.91 per sec.)
and by 4-5% on an Intel dual-core system too:
2.6.23:
1: transactions: 4560 (455.94 per sec.)
2: transactions: 10094 (1009.30 per sec.)
3: transactions: 9755 (975.36 per sec.)
4: transactions: 9859 (985.78 per sec.)
5: transactions: 9701 (969.72 per sec.)
2.6.23 + sys_time-speedup.patch:
1: transactions: 4779 (477.84 per sec.)
2: transactions: 10103 (1010.14 per sec.)
3: transactions: 10141 (1013.93 per sec.)
4: transactions: 10371 (1036.89 per sec.)
5: transactions: 10178 (1017.50 per sec.)
(the more CPUs the system has, the more speedup this patch gives for
this particular workload.)
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
---
kernel/time.c | 6 +-----
kernel/time/timekeeping.c | 7 -------
2 files changed, 1 insertion(+), 12 deletions(-)
Index: linux/kernel/time.c
===================================================================
--- linux.orig/kernel/time.c
+++ linux/kernel/time.c
@@ -57,11 +57,7 @@ EXPORT_SYMBOL(sys_tz);
*/
asmlinkage long sys_time(time_t __user * tloc)
{
- time_t i;
- struct timespec tv;
-
- getnstimeofday(&tv);
- i = tv.tv_sec;
+ time_t i = get_seconds();
if (tloc) {
if (put_user(i,tloc))
Index: linux/kernel/time/timekeeping.c
===================================================================
--- linux.orig/kernel/time/timekeeping.c
+++ linux/kernel/time/timekeeping.c
@@ -49,19 +49,12 @@ struct timespec wall_to_monotonic __attr
static unsigned long total_sleep_time; /* seconds */
EXPORT_SYMBOL(xtime);
-
-#ifdef CONFIG_NO_HZ
static struct timespec xtime_cache __attribute__ ((aligned (16)));
static inline void update_xtime_cache(u64 nsec)
{
xtime_cache = xtime;
timespec_add_ns(&xtime_cache, nsec);
}
-#else
-#define xtime_cache xtime
-/* We do *not* want to evaluate the argument for this case */
-#define update_xtime_cache(n) do { } while (0)
-#endif
static struct clocksource *clock; /* pointer to current clocksource */
-
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