linux-kernel - Re: [PATCH v10 04/11] sched: Make sched entity usage tracking scale-invariant

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Message-ID: <20150407133112.GB18994@e105550-lin.cambridge.arm.com>
Date:	Tue, 7 Apr 2015 14:31:12 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Mike Galbraith <efault@....de>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>
Subject: Re: [PATCH v10 04/11] sched: Make sched entity usage tracking
 scale-invariant

On Thu, Apr 02, 2015 at 06:32:38PM +0100, Peter Zijlstra wrote:
> 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 wouldn't have thought so, and it turned out not to be...

> 
> > 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?

Yes, of course, it works fine. It was just me missing the most obvious
solution. No need to include linux/sched.h, 'struct sched_domain;' was
the bit I was missing. Sorry for the noise.

> > 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?

The above works just fine, so no need for that anyway :)
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