linux-kernel - Re: [RFC PATCH v3 03/10] PM: Introduce an Energy Model management framework

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Message-ID: <20180619124058.GX17720@e108498-lin.cambridge.arm.com>
Date:   Tue, 19 Jun 2018 13:40:59 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rjw@...ysocki.net, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        mingo@...hat.com, dietmar.eggemann@....com,
        morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joelaf@...gle.com,
        smuckle@...gle.com, adharmap@...cinc.com, skannan@...cinc.com,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [RFC PATCH v3 03/10] PM: Introduce an Energy Model management
 framework

On Tuesday 19 Jun 2018 at 13:31:06 (+0200), Peter Zijlstra wrote:
> On Mon, May 21, 2018 at 03:24:58PM +0100, Quentin Perret wrote:
> > +	read_lock_irqsave(&em_data_lock, flags);
> > +	for_each_cpu(cpu, cpu_possible_mask) {
> 
> I know we're likely to only use this on small systems, but this pattern
> is a very bad, Please look at alternatives.

Ok, this isn't supposed to be called very often (only once, at boot
time, for Arm for example), but I see your point.