dev.cpu.0.freq disapeared

[Dmitry Sivachenko]

> On 22 марта 2015 г., at 8:53, Peter Jeremy <peter at rulingia.com> wrote:
> 
> On 2015-Mar-22 00:58:55 +0300, Dmitry Sivachenko <trtrmitya at gmail.com> wrote:
>> I have a machine with the following processor:
>> 
>> CPU: Intel(R) Xeon(R) CPU           E5620  @ 2.40GHz (2400.14-MHz K8-class CPU)
>> Origin="GenuineIntel"  Id=0x206c2  Family=0x6  Model=0x2c  Stepping=2
> ...
>> After I upgraded to 10.1-STABLE #0 r279956, this sysctl disapeared.
>> % sysctl dev.cpu.0.freq
>> sysctl: unknown oid 'dev.cpu.0.freq': No such file or directory
>> %
> 
> What OIDs do you have?  Does dev.cpu.0 exist?  How about dev.cpu?

dev.cpu.0 does exist.  

I found the problematic change:

Author: nwhitehorn
Date: Sun Jan 11 17:10:07 2015
New Revision: 276986
URL: https://svnweb.freebsd.org/changeset/base/276986

Log:
 MFC r265329:
 Disable ACPI and P4TCC throttling by default, following discussion on
 freebsd-current. These CPU speed control techniques are usually unhelpful
 at best. For now, continue building the relevant code into GENERIC so that
 it can trivially be re-enabled at runtime if anyone wants it.

Modified: stable/10/sys/amd64/conf/GENERIC.hints
==============================================================================
--- stable/10/sys/amd64/conf/GENERIC.hints	Sun Jan 11 17:00:24 2015	(r276985)
+++ stable/10/sys/amd64/conf/GENERIC.hints	Sun Jan 11 17:10:07 2015	(r276986)
@@ -31,3 +31,5 @@ hint.attimer.0.at="isa"
hint.attimer.0.port="0x40"
hint.attimer.0.irq="0"
hint.wbwd.0.at="isa"
+hint.acpi_throttle.0.disabled="1"
+hint.p4tcc.0.disabled="1"


If I remove that hint.p4tcc.0.disabled="1" from device.hints, dev.cpu.0.freq appears back again.

I am using dev.cpu.0.freq to ensure that processor is running at expected frequency (with some buggy BIOSes or buggy BIOS options combinations it is possible to end up with machine running at half frequency).

Does it really hurt to have this sysctl available?  Why it was disabled by default?

(I am not discussing  hint.acpi_throttle.0.disabled here, just hint.p4tcc.0.disabled).

Thanks.