On 03/22/15 09:29, Kevin Oberman wrote:
On Sun, Mar 22, 2015 at 7:11 AM, Ian Smith <smi...@nimnet.asn.au
<mailto:smi...@nimnet.asn.au>> wrote:
Dmitry Sivachenko wrote:
On 22 марта 2015 г., at 8:53, Peter Jeremy
<pe...@rulingia.com <mailto:pe...@rulingia.com>> wrote:
On 2015-Mar-22 00:58:55 +0300, Dmitry Sivachenko
<trtrmi...@gmail.com <mailto:trtrmi...@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.
It could be helpful to show all of:
% sysctl dev.cpu
% sysctl dev.est # if you have that?
% sysctl -a | grep freq | grep -v time
both before and after re-enabling p4tcc.
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
<http://hint.attimer.0.at>="isa" hint.attimer.0.port="0x40"
hint.attimer.0.irq="0" hint.wbwd.0.at
<http://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.
'Trivial re-enabling' would be adding hint.p4tcc.0.disabled="0" to
/boot/loader.conf. This seems very strange though, if it really is
due solely to disabling p4tcc and acpi_throttle.
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).
Are you not running powerd? Of course powerd won't start if it can't
get dev.cpu.0.freq but you can ordinarily use it to set lowest and/or
highest freqs. Once FreeBSD starts, BIOS settings should have little
do with it, AFAIK, except how they might set freq before powerd
starts.
Does it really hurt to have this sysctl available? Why it was
disabled by default?
It's a long story; (a) short story is using it to vary freqs doesn't
save any power, but makes powerd work harder matching freq to load.
(I am not discussing hint.acpi_throttle.0.disabled here, just
hint.p4tcc.0.disabled).
Some or many systems will use ACPI throttling instead if p4tcc (or
equivalent on AMD or other processors) isn't enabled, so they both
need disabling to run 'raw' EST or equivalent.
A link to a verbose boot would be good, before and after if possible.
cheers, Ian
First, my system which does have powerd and dev.cpu.0.freq has been
running without p4tcc for years. From my loader.conf file:
# Disable CPU throttling
hint.p4tcc.0.disabled=1
hint.acpi_throttle.0.disabled=1
But I do have EST. If that is missing, so is dev.cpu.0.freq. Do you
see "sysctl dev.est"? It should include freq_settings for each CPU.
Processors older than P4s did not have the more efficient TCC
capability, so the more primitive throttling was used. By default,
when TCC is available, it is used. If not, throttling is used. Of
course, almost all i386 and all amd64 processors should have TCC, so,
unless TCC is disabled, throttling is not used.
TCC is the Thermal Control Circuit. Note that it was designed and
intended to be a rather heavy handed way to prevent overheating of the
CPU. It was never intended nor is it useful for power management.
Worse, it can interfere with C-states, by far the most effective power
management tool available, at least when used the way powerd uses it.
This "unpleasant" interaction that lead to system lock-up resulted in
C-states being disabled, just adding insult to injury. Head should now
have the "correct" settings with throttling and p4tcc disabled and
both performance and economy_cx_lowest defaulting to Cmax.
The real issue appears to be that some systems seem to not have EST. I
am suspicious that this may be the case for some or all non-i386/amd64
processors. Even if EST is not available, turning on TCC or throttling
is not going to save any power. It just means that the system will not
have the ability to have multiple CPU frequencies.
Thanks for the nice summary. We do in fact have non-x86 CPUs with real
power management and EST-equivalent clock changing that are supported by
FreeBSD. I think the P4-era stuff is the only hardware that uses
throttling/TCC-type logic.
-Nathan
If you want more details on power issues in FreeBSD, I would point you
to the excellent article by mav@ at
https://wiki.freebsd.org/TuningPowerConsumption. He covers all of the
research I did independently back when I was at Lawrence Berkeley.Lab
back in the 90s and extends it to cover most modern technologies not
available when I did my research.
--
Kevin Oberman, Network Engineer, Retired
E-mail: rkober...@gmail.com <mailto:rkober...@gmail.com>
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