diff options
| author | Ingo Molnar <mingo@elte.hu> | 2007-07-16 08:41:18 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-07-16 18:05:48 +0200 |
| commit | 4e44f3497d41db4c3b9051c61410dee8ae4fb49c (patch) | |
| tree | 8c54919894c8f6ac629c6c28cee8fb504721d652 /kernel | |
| parent | is_power_of_2(): jbd (diff) | |
| download | linux-4e44f3497d41db4c3b9051c61410dee8ae4fb49c.tar.xz linux-4e44f3497d41db4c3b9051c61410dee8ae4fb49c.zip | |
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')
| -rw-r--r-- | kernel/time.c | 32 |
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 |