linux-kernel - Running an Ivy Bridge cpu at fixed frequency

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Message-ID: <8eeee0695c664305ba6a56bce42a995f@AcuMS.aculab.com>
Date:   Wed, 4 Dec 2019 17:01:32 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Running an Ivy Bridge cpu at fixed frequency

Is there any way to persuade the intel_pstate driver to make an Ivy bridge (i7-3770)
cpu run at a fixed frequency?
It is really difficult to compare code execution times when the cpu clock speed
keeps changing.
I thought I'd managed by setting the 'scaling_max_freq' to 1.7GHz, but even that
doesn't seem to be working now.
It would also be nice to run a little faster than that - but without it 'randomly'
going to 'turbo' frequencies (which it is doing even after I've set no_turbo to 1).

An alternative would be a variable frequency TSC - might give more consistent values.

	David

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