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Date: Thu, 2 Apr 2015 19:32:38 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
        Ingo Molnar <mingo@kernel.org>,
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        Linaro Kernel Mailman List <linaro-kernel@lists.linaro.org>,
        Paul Turner <pjt@google.com>, Ben Segall <bsegall@google.com>
Subject: Re: [PATCH v10 04/11] sched: Make sched entity usage tracking
 scale-invariant
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On Thu, Apr 02, 2015 at 05:53:09PM +0100, Morten Rasmussen wrote:
> Could you enlighten me a bit about how to define the arch specific
> implementation without getting into trouble? I'm failing miserably :(

Hmm, this was not supposed to be difficult.. :/

> I thought the arm arch-specific topology.h file was a good place to put
> the define as it get included in sched.h, so I did a:
> 
> #define arch_scale_freq_capacity arm_arch_scale_freq_capacity
> 
> However, I have to put a function prototype in the same (or some other
> included) header file to avoid doing an implicit function definition.
> arch_scale_freq_capacity() takes a struct sched_domain pointer, so I
> have to include linux/sched.h which leads to circular dependency between
> linux/sched.h and topology.h.

Why would you have to include linux/sched.h ?

#define arch_scale_freq_capacity arch_scale_freq_capacity
struct sched_domain;
extern unsigned long arch_scale_freq_capacity(struct sched_domain *, int cpu);

Would work from you asm/topology.h, right?

> We can drop the sched_domain pointer as we don't use it, but I'm going
> to do the same trick for arch_scale_cpu_capacity() as well which does
> require the sd pointer.

Sure, dropping that pointer is fine.

> Finally, is introducing an ARCH_HAS_SCALE_FREQ_CAPACITY or similar a
> complete no go?

It seems out of style, I'd have to go look for the email thread, but
this should more or less be the same no?