From owner-freebsd-net@freebsd.org  Tue Oct 20 08:24:54 2015
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Date: Tue, 20 Oct 2015 19:24:37 +1100 (EST)
From: Ian Smith <smithi@nimnet.asn.au>
To: Kevin Oberman <rkoberman@gmail.com>
cc: Luigi Rizzo <rizzo@iet.unipi.it>, "jfv@FreeBSD.org" <jfv@freebsd.org>,
 "ricera10@gmail.com" <ricera10@gmail.com>,
 "Eggert, Lars" <lars@netapp.com>,
 Giuseppe Lettieri <g.lettieri@iet.unipi.it>,
 "net@freebsd.org" <net@freebsd.org>
Subject: Re: ixl 40G bad performance?
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On Mon, 19 Oct 2015 21:47:36 -0700, Kevin Oberman wrote:
 > > I suspect it might not touch the c states, but better check. The safest is
 > > disable them in the bios.
 > >
 > 
 > To disable C-States:
 > sysctl dev.cpu.0.cx_lowest=C1

Actually, you want to set hw.acpi.cpu.cx_lowest=C1 instead.  Otherwise 
you've only changed cpu.0; if you try it you should see that other CPUs 
will have retained their previous C-state setting - up to 9.3 at least.

Setting performance_cx_lowest=C1 in rc.conf (and economy_cx_lowest=C1 on 
laptops) performs that by setting hw.acpi.cpu.cx_lowest on boot (and on 
every change to/from battery power) in power_profile via devd notifies.

cheers, Ian