linux-kernel - Re: [PATCH v7] timekeeping: Added a function to return tv_sec portion of ktime_get

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Message-ID: <3371590.dCyFlG7rJg@wuerfel>
Date:	Wed, 29 Oct 2014 10:37:42 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Heena Sirwani <heenasirwani@...il.com>,
	linux-kernel@...r.kernel.org, john.stultz@...aro.org
Subject: Re: [PATCH v7] timekeeping: Added a function to return tv_sec portion of ktime_get_ts64()

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
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