time: introduce xtime_seconds
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 <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -57,11 +57,7 @@ EXPORT_SYMBOL(sys_tz);
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*/
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asmlinkage long sys_time(time_t __user * tloc)
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{
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time_t i;
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struct timespec tv;
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getnstimeofday(&tv);
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i = tv.tv_sec;
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time_t i = get_seconds();
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if (tloc) {
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if (put_user(i,tloc))
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@ -49,19 +49,12 @@ struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
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static unsigned long total_sleep_time; /* seconds */
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EXPORT_SYMBOL(xtime);
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#ifdef CONFIG_NO_HZ
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static struct timespec xtime_cache __attribute__ ((aligned (16)));
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static inline void update_xtime_cache(u64 nsec)
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{
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xtime_cache = xtime;
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timespec_add_ns(&xtime_cache, nsec);
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}
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#else
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#define xtime_cache xtime
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/* We do *not* want to evaluate the argument for this case */
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#define update_xtime_cache(n) do { } while (0)
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#endif
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static struct clocksource *clock; /* pointer to current clocksource */
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