Re: [RFC 1/8] Implement getnsboottime kernel API

[Zachary Amsden <zamsden@redhat.com>]

On 08/30/2010 06:06 AM, Glauber Costa wrote:
> From: Zachary Amsden<zamsden@redhat.com>
>
> Add a kernel call to get the number of nanoseconds since boot.  This
> is generally useful enough to make it a generic call.
>
> Signed-off-by: Zachary Amsden<zamsden@redhat.com>
> ---
>   include/linux/time.h      |    1 +
>   kernel/time/timekeeping.c |   27 +++++++++++++++++++++++++++
>   2 files changed, 28 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/time.h b/include/linux/time.h
> index ea3559f..5d04108 100644
> --- a/include/linux/time.h
> +++ b/include/linux/time.h
> @@ -145,6 +145,7 @@ extern void getnstimeofday(struct timespec *tv);
>   extern void getrawmonotonic(struct timespec *ts);
>   extern void getboottime(struct timespec *ts);
>   extern void monotonic_to_bootbased(struct timespec *ts);
> +extern s64 getnsboottime(void);
>
>   extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
>   extern int timekeeping_valid_for_hres(void);
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index caf8d4d..d250f0a 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -285,6 +285,33 @@ void ktime_get_ts(struct timespec *ts)
>   }
>   EXPORT_SYMBOL_GPL(ktime_get_ts);
>
> +
> +/**
> + * getnsboottime - get the bootbased clock in nsec format
> + *
> + * The function calculates the bootbased 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.
> + */
> +s64 getnsboottime(void)
> +{
> +	unsigned int seq;
> +	s64 secs, nsecs;
> +
> +	WARN_ON(timekeeping_suspended);
> +
> +	do {
> +		seq = read_seqbegin(&xtime_lock);
> +		secs = xtime.tv_sec + wall_to_monotonic.tv_sec;
> +		secs += total_sleep_time.tv_sec;
> +		nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
> +		nsecs += total_sleep_time.tv_nsec + timekeeping_get_ns();
> +
> +	} while (read_seqretry(&xtime_lock, seq));
> +	return nsecs + (secs * NSEC_PER_SEC);
> +}
> +EXPORT_SYMBOL_GPL(getnsboottime);
> +
>   /**
>    * do_gettimeofday - Returns the time of day in a timeval
>    * @tv:		pointer to the timeval to be set
>    

FWIW, I sent a patch to drop this yesterday, in favor of this approach:

+static inline u64 get_kernel_ns(void)
+{
+    struct timespec ts;
+
+    WARN_ON(preemptible());
+    ktime_get_ts(&ts);
+    monotonic_to_bootbased(&ts);
+    return timespec_to_ns(&ts);
+}
+