Messages in this thread | | | Subject | Re: [PATCH] optimized ktime_get[_ts] for GENERIC_TIME=y | From | john stultz <> | Date | Mon, 06 Jul 2009 11:41:24 -0700 |
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On Mon, 2009-07-06 at 15:49 +0200, Martin Schwidefsky wrote: > From: Martin Schwidefsky <schwidefsky@de.ibm.com> > > The generic ktime_get function defined in kernel/hrtimer.c is suboptimial > for GENERIC_TIME=y: > > 0) | ktime_get() { > 0) | ktime_get_ts() { > 0) | getnstimeofday() { > 0) | read_tod_clock() { > 0) 0.601 us | } > 0) 1.938 us | } > 0) | set_normalized_timespec() { > 0) 0.602 us | } > 0) 4.375 us | } > 0) 5.523 us | } > > Overall there are two read_seqbegin/read_seqretry loops and a lot of > unnecessary struct timespec calculations. ktime_get returns a nano second > value which is the sum of xtime, wall_to_monotonic and the nano second > delta from the clock source. > > ktime_get can be optimized for GENERIC_TIME=y. The new version only calls > clocksource_read: > > 0) | ktime_get() { > 0) | read_tod_clock() { > 0) 0.610 us | } > 0) 1.977 us | } > > It uses a single read_seqbegin/readseqretry loop and just adds everthing > to a nano second value. > > ktime_get_ts is optimized in a similar fashion. > > Cc: Ingo Molnar <mingo@elte.hu> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: john stultz <johnstul@us.ibm.com> > Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Looks good to me. Acked-by: John Stultz <johnstul@us.ibm.com>
> --- > kernel/hrtimer.c | 4 ++ > kernel/time/timekeeping.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 67 insertions(+) > > > diff -urpN linux-2.5/kernel/hrtimer.c linux-2.5-patched/kernel/hrtimer.c > --- linux-2.5/kernel/hrtimer.c 2009-07-03 10:46:07.000000000 +0200 > +++ linux-2.5-patched/kernel/hrtimer.c 2009-07-03 10:46:23.000000000 +0200 > @@ -46,6 +46,7 @@ > > #include <asm/uaccess.h> > > +#ifndef CONFIG_GENERIC_TIME > /** > * ktime_get - get the monotonic time in ktime_t format > * > @@ -60,6 +61,7 @@ ktime_t ktime_get(void) > return timespec_to_ktime(now); > } > EXPORT_SYMBOL_GPL(ktime_get); > +#endif > > /** > * ktime_get_real - get the real (wall-) time in ktime_t format > @@ -104,6 +106,7 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, > } > }; > > +#ifndef CONFIG_GENERIC_TIME > /** > * ktime_get_ts - get the monotonic clock in timespec format > * @ts: pointer to timespec variable > @@ -128,6 +131,7 @@ void ktime_get_ts(struct timespec *ts) > ts->tv_nsec + tomono.tv_nsec); > } > EXPORT_SYMBOL_GPL(ktime_get_ts); > +#endif > > /* > * Get the coarse grained time at the softirq based on xtime and > diff -urpN linux-2.5/kernel/time/timekeeping.c linux-2.5-patched/kernel/time/timekeeping.c > --- linux-2.5/kernel/time/timekeeping.c 2009-07-03 10:46:07.000000000 +0200 > +++ linux-2.5-patched/kernel/time/timekeeping.c 2009-07-03 10:46:23.000000000 +0200 > @@ -118,6 +118,69 @@ void getnstimeofday(struct timespec *ts) > > EXPORT_SYMBOL(getnstimeofday); > > +ktime_t ktime_get(void) > +{ > + cycle_t cycle_now, cycle_delta; > + struct timespec time; > + unsigned long seq; > + s64 nsecs; > + > + do { > + seq = read_seqbegin(&xtime_lock); > + time.tv_sec = xtime.tv_sec + wall_to_monotonic.tv_sec; > + time.tv_nsec = xtime.tv_nsec + wall_to_monotonic.tv_nsec; > + > + /* read clocksource: */ > + cycle_now = clocksource_read(clock); > + > + /* calculate the delta since the last update_wall_time: */ > + cycle_delta = (cycle_now - clock->cycle_last) & clock->mask; > + > + /* convert to nanoseconds: */ > + nsecs = cyc2ns(clock, cycle_delta); > + > + } while (read_seqretry(&xtime_lock, seq)); > + nsecs += time.tv_sec * 1000000000ULL + time.tv_nsec; > + return (ktime_t) { .tv64 = nsecs }; > +} > +EXPORT_SYMBOL_GPL(ktime_get); > + > +/** > + * ktime_get_ts - get the monotonic clock in timespec format > + * @ts: pointer to timespec variable > + * > + * The function calculates the monotonic clock from the realtime > + * clock and the wall_to_monotonic offset and stores the result > + * in normalized timespec format in the variable pointed to by @ts. > + */ > +void ktime_get_ts(struct timespec *ts) > +{ > + cycle_t cycle_now, cycle_delta; > + struct timespec tomono; > + unsigned long seq; > + s64 nsecs; > + > + do { > + seq = read_seqbegin(&xtime_lock); > + *ts = xtime; > + tomono = wall_to_monotonic; > + > + /* read clocksource: */ > + cycle_now = clocksource_read(clock); > + > + /* calculate the delta since the last update_wall_time: */ > + cycle_delta = (cycle_now - clock->cycle_last) & clock->mask; > + > + /* convert to nanoseconds: */ > + nsecs = cyc2ns(clock, cycle_delta); > + > + } while (read_seqretry(&xtime_lock, seq)); > + > + set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec, > + ts->tv_nsec + tomono.tv_nsec + nsecs); > +} > +EXPORT_SYMBOL_GPL(ktime_get_ts); > + > /** > * do_gettimeofday - Returns the time of day in a timeval > * @tv: pointer to the timeval to be set > >
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