sys_time() speedup (4e44f349) · Commits · 戴 / test

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>

kernel/time.c

+24 −8

Original line number	Diff line number	Diff line
		@@ -57,11 +57,14 @@ 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))
		@@ -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

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