linux-kernel - Re: [PATCH 1/5] split clocksource adjustment from clockosurce mult

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Date:	Fri, 14 Mar 2008 22:07:00 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 1/5] split clocksource adjustment from clockosurce mult


On Sat, 2008-03-15 at 05:28 +0100, Roman Zippel wrote:
> Hi,
> 
> On Fri, 14 Mar 2008, john stultz wrote:
> 
> > @@ -179,7 +181,7 @@ static inline cycle_t clocksource_read(struct clocksource *cs)
> >  static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
> >  {
> >  	u64 ret = (u64)cycles;
> > -	ret = (ret * cs->mult) >> cs->shift;
> > +	ret = (ret * (cs->mult + cs->mult_adj)) >> cs->shift;
> >  	return ret;
> >  }
> 
> This add an extra memory access and extra instruction to a code path, we 
> should keep as short as possible.
> I'd rather add a mult_raw or mult_org and use that for your next patch.

Yea, I played with that at first, but the functoinal duplication (two
values, both storing close to the same info) was ugly. 

I guess I could go back to mult_orig.

-john


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