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Date:      Mon, 5 May 2014 10:53:45 +0200
From:      Fabian Keil <freebsd-listen@fabiankeil.de>
To:        "freebsd-acpi@freebsd.org" <freebsd-acpi@freebsd.org>
Cc:        "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org>
Subject:   Re: proposal: set default lid state to S3, performance/economy Cx states to Cmax
Message-ID:  <20140505105345.099e4503@fabiankeil.de>
In-Reply-To: <alpine.BSF.2.00.1405041829030.9604@wonkity.com>
References:  <CAJ-Vmo=mUtpjgVwNHg8af05vCxVchZdsaekR9_Wf-pOfFjnABQ@mail.gmail.com> <FCE7DE37-81D4-4859-98DF-89E606B29CAC@felyko.com> <alpine.BSF.2.00.1405041641290.9118@wonkity.com> <CAJ-Vmo=aWmrxYPq9znwwi3C4wqf%2B_Q0DE3eLjmNMuHXVDnLHfA@mail.gmail.com> <alpine.BSF.2.00.1405041829030.9604@wonkity.com>

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Warren Block <wblock@wonkity.com> wrote:

> On Sun, 4 May 2014, Adrian Chadd wrote:

> > The easy-to-run test is "sysctl dev.cpu.0.cx_lowest=3DCmax" and then us=
e stuff.
>=20
> It's that "use stuff" step that would preferably be automated.  Is the=20
> failure mode a lockup, or could a program detect problems?  The idea=20
> is to get lots of feedback, fast.

One possible failure mode is that timers tick unreliably which can be
detected automatically (in some cases), for example by using the DTrace
script timestamp-test.d:
http://www.fabiankeil.de/gehacktes/dtrace-timestamp-tests/

It should also be possible to let the kernel do this itself
and log an error message and maybe optionally disable Cx
states that cause problems:
sysctl dev.cpu.0.cx_lowest=3DCmax-as-long-as-it-appears-to-be-working

Fabian

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