linux-kernel - Re: [PATCH v5] timekeeping: Added a function to return tv_sec portion of ktime_get

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Message-ID: <alpine.DEB.2.11.1410251705550.5308@nanos>
Date:	Sat, 25 Oct 2014 17:12:48 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Heena Sirwani <heenasirwani@...il.com>
cc:	linux-kernel@...r.kernel.org, john.stultz@...aro.org, arnd@...db.de
Subject: Re: [PATCH v5] timekeeping: Added a function to return tv_sec portion
 of ktime_get_ts64()

On Sat, 25 Oct 2014, Heena Sirwani wrote:
> +time64_t ktime_get_seconds(void)
> +{
> +	time64_t ts;
> +	struct timekeeper *tk = &tk_core.timekeeper;
> +	struct timespec64 tomono;
> +	s32 nsec;
> +	unsigned int seq;
> +
> +	WARN_ON(timekeeping_suspended);
> +
> +	do {
> +		seq = read_seqcount_begin(&tk_core.seq);
> +		ts = tk->xtime_sec;
> +		nsec = (long)(tk->tkr.xtime_nsec >> tk->tkr.shift);
> +		tomono = tk->wall_to_monotonic;
> +
> +	} while (read_seqcount_retry(&tk_core.seq, seq));
> +
> +	ts += tomono.tv_sec;
> +	if (nsec + tomono.tv_nsec >= NSEC_PER_SEC)
> +		ts += 1;
> +	return ts;

I'd rather have an extra field in the timekeeper

    u64 xtime_sec;
+   u64 ktime_sec;

and update this in tk_update_ktime_data() so the readout function
boils down to

time64_t ktime_get_seconds(void)
{
#if BITS_PER_LONG < 64
	u64 sec;
	int seq;

	do {
		seq = read_seqcount_begin(&tk_core.seq);
		sec = tk->ktime_sec;
	} while (read_seqcount_retry(&tk_core.seq, seq));

	return sec;
#else
	return tk->ktime_sec;
#endif
}

So 64bit can do w/o the seqcount and 32bit avoids all extra math, right?

Thanks,

	tglx
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