linux-kernel - What should cpuinfo_cur

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Message-ID: <CALCETrVncODPCEU9_a7npHZdK-MJXJ3s7g1xsBacOW4Frxp+jA@mail.gmail.com>
Date:	Mon, 10 Feb 2014 12:47:12 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Naga Chumbalkar <nagananda.chumbalkar@...com>,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: What should cpuinfo_cur_freq mean?

There are least three choices for what the "current frequency" is:

 1. The frequency that the cpufreq driver thinks it has requested.
This shows up in scaling_cur_freq.

 2. The frequency that is actually programmed into the CPU.  This is
what acpi_cpufreq's cpuinfo_cur_freq reports.

 3. A measurement of the number of cycles per unit time that are
currently or recently happening.  This is what intel_pstate reports.

The fact that acpi-cpufreq and intel_pstate behave differently here is
unfortunate.  I have servers [1] with broken BIOS that occasionally
screw up the requested P-state (i.e. MSR 0x199).  With acpi_cpufreq
loaded, I can at least tell that there's a problem by reading
cpuinfo_cur_freq.  With intel_pstate loaded, I get a rapidly
fluctuating value that depends on Turbo's current mood.

Can we separate out these concepts into separate sysfs files?

[1] These are fully up-to-date, recent generation Dell servers.
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