linux-kernel - Re: [RFC][patch 4/5] clocksource_read/clocksource_read

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Message-ID: <20090722092934.4fa16eba@skybase>
Date:	Wed, 22 Jul 2009 09:29:34 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	john stultz <johnstul@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][patch 4/5] clocksource_read/clocksource_read_raw inline
 functions

On Tue, 21 Jul 2009 15:01:14 -0700
john stultz <johnstul@...ibm.com> wrote:

> On Tue, 2009-07-21 at 21:17 +0200, Martin Schwidefsky wrote:
> > plain text document attachment (clocksource-read-ns.diff)
> > From: Martin Schwidefsky <schwidefsky@...ibm.com>
> > 
> > Add clocksource_read / clocksource_read_raw inline functions and use
> > them for getnstimeofday, ktime_get, ktime_get_ts and getrawmonotonic.
> > 
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: john stultz <johnstul@...ibm.com>
> > Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> > ---
> >  include/linux/clocksource.h |   45 +++++++++++++++++++++++++++++++++++++++++++
> >  kernel/time/timekeeping.c   |   46 +++-----------------------------------------
> >  2 files changed, 49 insertions(+), 42 deletions(-)
> > 
> > Index: linux-2.6/include/linux/clocksource.h
> > ===================================================================
> > --- linux-2.6.orig/include/linux/clocksource.h
> > +++ linux-2.6/include/linux/clocksource.h
> > @@ -284,6 +284,51 @@ static inline s64 cyc2ns(struct clocksou
> >  	return ret;
> >  }
> > 
> > +/**
> > + * clocksource_read: - Read nanosecond delta from clocksource.
> > + * @cs:		pointer to clocksource being read
> > + *
> > + * Read from the clock source and return the clock value converted
> > + * to nanoseconds.
> > + */
> > +static inline s64 clocksource_read(struct clocksource *cs)
> > +{
> > +	cycle_t cycle_now, cycle_delta;
> > +
> > +	/* read clocksource: */
> > +	cycle_now = cs->read(cs);
> > +
> > +	/* calculate the delta since the last update_wall_time: */
> > +	cycle_delta = (cycle_now - cs->cycle_last) & cs->mask;
> > +
> > +	/* convert to nanoseconds: */
> > +	return cyc2ns(cs, cycle_delta);
> > +}
> 
> Oof. So you took out clocksource_read() only to replace with a different
> function with the same name? If this move is necessary, could we call
> these clocksource_get_ns()/clocksource_get_raw_ns() to avoid the
> confusion?

The code that uses the old clocksource_read is accessing other fields
from the struct clocksource. So the old inline function seems
redundant to me. The new one do more and returns a value where you
don't need anything else from the clocksource (namely nanoseconds).
To reuse the name adds a little confusion while you look at the patches,
the end result should be pretty clear, no? But if you prefer to add the
_ns suffix that is fine with me.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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