linux-kernel - Re: [PATCH] PM / arch: x86: Rework the MSR_IA32_ENERGY_PERF

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Message-ID: <CAJZ5v0hz3KFtmsP+8Qbee7KrV4BBOUzReUmK8BWH52+hwekt=Q@mail.gmail.com>
Date:   Thu, 21 Mar 2019 10:21:15 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Laura Abbott <labbott@...oraproject.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Simon Schricker <sschricker@...e.de>,
        Borislav Petkov <bp@...e.de>, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH] PM / arch: x86: Rework the MSR_IA32_ENERGY_PERF_BIAS handling

On Thu, Mar 21, 2019 at 8:58 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Mar 21, 2019 at 01:00:52AM +0100, Rafael J. Wysocki wrote:
> > + * The Performance and Energy Bias Hint (EPB) allows software to specify its
> > + * preference with respect to the power-performance tradeoffs present in the
> > + * processor.  Generally, the EPB is expected to be set by user space through
> > + * the generic MSR interface (with the help of the x86_energy_perf_policy tool),
> > + * but there are two reasons for the kernel to touch it.
>
> So I hate /dev/msr with a passion. It is absolute atrocious crap.
>
> Please, just make a real interface for this if it is important.

That's the plan going forward, this is just documenting the current situation.

Do you have any particular concerns regarding this patch?