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

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Date:	Wed, 29 Oct 2014 10:40:00 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arnd Bergmann <arnd@...db.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 Wed, 29 Oct 2014, Arnd Bergmann wrote:

> 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?

136 years uptime :) I think we discussed that 32bit thing before, but
I forgot again.
 
> 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.

Indeed.

Thanks,

	tglx
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