Date: Thu, 18 Nov 2010 16:10:38 +0200 From: Andriy Gapon <avg@freebsd.org> To: Daniel Nebdal <dnebdal@gmail.com> Cc: George Neville-Neil <gnn@neville-neil.com>, freebsd-current@freebsd.org, freebsd-acpi@freebsd.org Subject: Re: aperf/mperf Message-ID: <4CE533DE.7010401@freebsd.org> In-Reply-To: <AANLkTimcJFL8Y47mTznKz72w0z5%2BVoc9oWrz92kE%2BwQa@mail.gmail.com> References: <4CE29718.2050508@freebsd.org> <D1DB20AD-779E-469B-BFFA-C0BA1A249858@neville-neil.com> <4CE51CDA.6010202@freebsd.org> <AANLkTimcJFL8Y47mTznKz72w0z5%2BVoc9oWrz92kE%2BwQa@mail.gmail.com>
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on 18/11/2010 15:38 Daniel Nebdal said the following: > Just for the sake of gathering information here: > What they offer are two (64-bit, wrapping) counters; one that > increases at a constant rate, and one that increases in proportion to > the current performance of the CPU, so that APERF/MPERF = fraction of > max possible performance the CPU has offered since the last time the > counters were zeroed. Intel specifically suggests multiplying that > with the observed CPU load over the same time period to get an > absolute CPU load number, and using that to pick a suitable P-state. > > On a tangent, I wonder if you can get APERF>MPERF if you're using an > i5/i7 and their dynamic/automatic overclocking kicks in? Yes, I believe so. At the very least AMD explicitly documents that to be the case when Core Performance Boost feature is activated. > As for what to do with it, it sounds like it would make sense as an > alternate data source for powerd? Yes, indeed. -- Andriy Gapon
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