Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755059AbZGFNtm (ORCPT ); Mon, 6 Jul 2009 09:49:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752954AbZGFNtd (ORCPT ); Mon, 6 Jul 2009 09:49:33 -0400 Received: from mtagate1.de.ibm.com ([195.212.17.161]:58738 "EHLO mtagate1.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752053AbZGFNtc (ORCPT ); Mon, 6 Jul 2009 09:49:32 -0400 Date: Mon, 6 Jul 2009 15:49:33 +0200 From: Martin Schwidefsky To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Thomas Gleixner , john stultz Subject: [PATCH] optimized ktime_get[_ts] for GENERIC_TIME=y Message-ID: <20090706154933.5a1f8990@skybase> Organization: IBM Corporation X-Mailer: Claws Mail 3.7.1 (GTK+ 2.16.3; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4917 Lines: 165 From: Martin Schwidefsky 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 Cc: Thomas Gleixner Cc: john stultz Signed-off-by: Martin Schwidefsky --- 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 +#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 -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/