linux-kernel - Re: [PATCH v4 8/8] arm,arm64,drivers: add a prefix to drivers arch

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Message-ID: <20170529095818.GA9892@kroah.com>
Date:   Mon, 29 May 2017 11:58:18 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, peterz@...radead.org,
        vincent.guittot@...aro.org, robh+dt@...nel.org,
        mark.rutland@....com, linux@....linux.org.uk, sudeep.holla@....com,
        lorenzo.pieralisi@....com, catalin.marinas@....com,
        will.deacon@....com, morten.rasmussen@....com, broonie@...nel.org
Subject: Re: [PATCH v4 8/8] arm,arm64,drivers: add a prefix to drivers
 arch_topology interfaces

On Mon, May 29, 2017 at 11:20:24AM +0200, Dietmar Eggemann wrote:
> Hi Greg,
> 
> On 05/26/2017 08:36 PM, Greg KH wrote:
> > On Fri, May 26, 2017 at 11:10:32AM +0100, Juri Lelli wrote:
> > > Hi,
> > > 
> > > On 25/05/17 15:18, Greg KH wrote:
> > > > On Thu, Apr 20, 2017 at 03:43:16PM +0100, Juri Lelli wrote:
> 
> [...]
> 
> > > > But this is all really topology stuff, right?  Why use "capacity" at
> > > > all:
> > > > 	topology_normalize_cpu()
> > > > 	topology_parse_cpu()
> > > > 	topology_scale_cpu()
> > > > 	topology_set_scale()
> > > > ?
> > > > 
> > > > It's always best to put the "subsystem" name first, we have a bad
> > > > history of getting this wrong in the past by putting the verb first, not
> > > > the noun.
> > > > 
> > > 
> > > topology_ works for me. However, I'd keep "capacity" in the names, as we
> > > might need to topology_normalize_cpu_somethingelse() (etc.) in the
> > > future?
> > 
> > Worry about the future, in the future.  Change the names then, _IF_ it
> > becomes an issue.  Try to be short and simple please.
> > 
> > > Updated patch follows. I kept Catalin and Russell's acks as I only
> > > renamed the functions, please shout if that's not OK.
> > > 
> > > Greg, if you are fine with this approach, do you still want a complete
> > > v5 of the set or can you pick this up?
> > 
> > Am I the one who is supposed to take all of these arm-specific patches?
> > If so, that's fine, but I need to have acks from the arm maintainers...
> > 
> > Oh, and drop "capacity" please :)
> 
> Once we have driver/base/arch_topology.c in, we want to enable (cpu
> micro-architectural + max frequency (OPPmax)) invariant and frequency
> (OPPmin..OPPmax) invariant load-tracking/accounting in the task scheduler
> for arm and arm64.
> 
> The way to do this is to define the task scheduler interfaces
> arch_scale_cpu_capacity() and arch_scale_freq_capacity() in arch specific
> code:
> 
> #define arch_scale_cpu_capacity topology_scale_cpu_capacity
> #define arch_scale_freq_capacity topology_scale_freq_capacity
> 
> In case an arch is not defining them, the default definitions in
> kernel/sched/sched.h are used.
> 
> So topology_scale_cpu() wouldn't be correct since we scale the _capacity_ by
> the micro-architectural differences (hence cpu) and not the cpu.
> 
> Likewise we will have a function topology_scale_freq_capacity indicating
> that we scale the capacity by the frequency.
> 
> Or would you prefer something like topology_scale_capacity_by_cpu() and
> topology_scale_capacity_by_freq()?

I think that if you are creating an api that the scheduler will use, you
need to ask the scheduler maintainers/developers what they want to see
here, as that would be up to them, not me...

thanks,

greg k-h