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

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Message-ID: <20180619113408.GQ2458@hirez.programming.kicks-ass.net>
Date:   Tue, 19 Jun 2018 13:34:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
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 Mon, May 21, 2018 at 03:24:58PM +0100, Quentin Perret wrote:
> +struct em_freq_domain *em_cpu_get(int cpu)
> +{
> +	struct em_freq_domain *fd;
> +	unsigned long flags;
> +
> +	read_lock_irqsave(&em_data_lock, flags);
> +	fd = per_cpu(em_data, cpu);
> +	read_unlock_irqrestore(&em_data_lock, flags);

Why can't this use RCU? This is the exact thing read_locks are terrible
at and RCU excells at.

> +
> +	return fd;
> +}
> +EXPORT_SYMBOL_GPL(em_cpu_get);