linux-kernel - Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160316200752.GJ6344@twins.programming.kicks-ass.net>
Date:	Wed, 16 Mar 2016 21:07:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dietmar Eggemann <dietmar.eggemann@....com>
Cc:	Michael Turquette <mturquette@...libre.com>, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Juri.Lelli@....com, steve.muckle@...aro.org,
	morten.rasmussen@....com, vincent.guittot@...aro.org,
	Michael Turquette <mturquette+renesas@...libre.com>
Subject: Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity

On Wed, Mar 16, 2016 at 07:44:33PM +0000, Dietmar Eggemann wrote:
> intel_pstate (setpolicy()) is an exception but my humble guess is that
> systems with intel_pstate driver have X86_FEATURE_APERFMPERF support.

A quick browse of the Intel SDM says you're right. It looks like
everything after Pentium-M; so Core-Solo/Core-Duo and onwards have
APERF/MPERF.

And it looks like P6 class systems didn't have DVFS support at all,
which basically leaves P4 and Pentium-M as the only chips to have DVFS
support lacking APERF/MPERF.

And while I haven't got any P4 based space heaters left, I might still
have a Pentium-M class laptop somewhere (if it still boots).