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Date: Thu, 26 Mar 2015 17:51:26 +0000
From: Morten Rasmussen <morten.rasmussen@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
        Ingo Molnar <mingo@kernel.org>,
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Subject: Re: [PATCH v10 04/11] sched: Make sched entity usage tracking
 scale-invariant
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On Thu, Mar 26, 2015 at 05:47:00PM +0000, Peter Zijlstra wrote:
> On Thu, Mar 26, 2015 at 05:38:45PM +0000, Morten Rasmussen wrote:
> > Another potential solution is to stay with weak functions but move the
> > multiplication and shift into the arch_scale_*() functions by passing
> > the value we want to scale into the arch_scale_*() function. That way we
> > can completely avoid multiplication and shift in the default case (no
> > arch_scale*() implementations, which is better than what we have today.
> > 
> > The only downside is that for frequency invariance we need three
> > arch_scale_freq_capacity() calls instead of two.
> 
> That would still result in unconditional function calls, which on some
> archs are _more_ expensive than 64bit mults.

Right. Then it can only be preprocessor magic I think.