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From: Arnd Bergmann <arnd@arndb.de>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Heena Sirwani <heenasirwani@gmail.com>, linux-kernel@vger.kernel.org,
        john.stultz@linaro.org
Subject: Re: [PATCH v7] timekeeping: Added a function to return tv_sec portion of ktime_get_ts64()
Date: Wed, 29 Oct 2014 10:37:42 +0100
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On Wednesday 29 October 2014 10:21:18 Thomas Gleixner wrote:
> On Wed, 29 Oct 2014, Heena Sirwani wrote:
> > +time64_t ktime_get_seconds(void)
> > +{
> > +     time64_t seconds;
> > +     struct timekeeper *tk = &tk_core.timekeeper;
> > +     unsigned int seq;
> > +
> > +     WARN_ON(timekeeping_suspended);
> 
> You want to have the same 64bit logic as you did for
> ktime_get_real_seconds. So on 64bit it boils down to return
> tk->ktime_sec.
> 
> > +
> > +     do {
> > +             seq = read_seqcount_begin(&tk_core.seq);
> > +             seconds = tk->ktime_sec;
> > +
> > +     } while (read_seqcount_retry(&tk_core.seq, seq));
> 

I wonder if we should just make tk->ktime_sec 'unsigned long' and
avoid the lock for 32-bit as well. Are there any theoretical
cases where the monotonic time could overflow a 32-bit integer?

As a minor optimization 's64 nsec_offset' could also be 'long',
since that only stores a number that is known to be less than
1000000000.

	Arnd