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From: Arthur Machlas on 29 Jul 2010 00:20
Greetings,

According to the spec sheet on the Atom N450 it has a single core,
though it does support two threads. However, linuxinfo (replaces
cpuinfo I suppose) says two unknown processors.

root(a)HPm210:/home/arthur/Misc/Linux/2.6.34-1# linuxinfo
Linux HPm210 2.6.32-5-686 #1 SMP Tue Jun 1 04:59:47 UTC 2010
Two Intel Unknown 1666MHz processors, 6650.42 total bogomips, 1011M RAM

Strangely, that's not the correct amount of ram in the system.

root(a)HPm210:/home/arthur/Misc/Linux/2.6.34-1# free -m
total used free shared buffers cached
Mem: 2014 1377 636 0 6 1186
-/+ buffers/cache: 184 1830
Swap: 1972 0 1971

Anyway, as you can see from the current directory, the reason I'm
asking about the number of cpu's cores in the atom n450 is that I'm
rolling my own kernel hoping a newer version will be able to get the
freq down to 800mhz same as windows, currently reporting that it can
only go as low as 1000. Also want to optimize for the atom processor
and build in all modules needed for hardware.

The Linux Kernel in a Nutshell book has got me pretty far, but I can't
solve this cpu thing and hoping someone can weigh in with some
friendly advice. The help in kernel config says things will run better
if I don't enable smp on a single cpu system. Hence, the question to
you, lazyweb, with much appreciation in advance.


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From: Stan Hoeppner on 29 Jul 2010 06:50
Arthur Machlas put forth on 7/28/2010 11:14 PM:
> Greetings,
>
> According to the spec sheet on the Atom N450 it has a single core,
> though it does support two threads. However, linuxinfo (replaces
> cpuinfo I suppose) says two unknown processors.

Your kernel doesn't either doesn't support CPU_ID or doesn't have the tables
for Atom CPUs, or both. This is a kernel config option.

> root(a)HPm210:/home/arthur/Misc/Linux/2.6.34-1# linuxinfo
> Linux HPm210 2.6.32-5-686 #1 SMP Tue Jun 1 04:59:47 UTC 2010
> Two Intel Unknown 1666MHz processors, 6650.42 total bogomips, 1011M RAM

> Strangely, that's not the correct amount of ram in the system.

Strangely, most people don't rely on linuxinfo. ;) File a bug report.

> root(a)HPm210:/home/arthur/Misc/Linux/2.6.34-1# free -m
> total used free shared buffers cached
> Mem: 2014 1377 636 0 6 1186
> -/+ buffers/cache: 184 1830
> Swap: 1972 0 1971
>
> Anyway, as you can see from the current directory, the reason I'm
> asking about the number of cpu's cores in the atom n450 is that I'm
> rolling my own kernel hoping a newer version will be able to get the
> freq down to 800mhz same as windows, currently reporting that it can
> only go as low as 1000. Also want to optimize for the atom processor
> and build in all modules needed for hardware.

In "make menuconfig":

In "Processor Type and Features"
uncheck Symmetric multi-processing support
check Intel Atom in "Processor Family"
check SMT (HyperThreading)
uncheck Multi-core scheduler support
check Intel MCE features
check /dev/cpu/*/msr - Model-specific register support
check /dev/cpu/*/cpuid - CPU information support

These last two are probably the reason for the "unknown", especially given
you're running 2.6.34 which has all the CPU models currently on the market.

In "Power management and ACPI options"
select "CPU Frequency scaling"
check CPU Frequency scaling (not a dup typo)
read the descriptions and decide which is the best default governor for you
then select the "CPUFreq processor drivers" that matches your hardware platform

You'll have to figure out all the other menu config settings on your own, as
most of us kernel monkeys have. ;) These are simply the ones that directly
relate to your questions.

Hope this helped get you closer.

--
Stan


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From: Arthur Machlas on 29 Jul 2010 13:10
On Thu, Jul 29, 2010 at 5:46 AM, Stan Hoeppner <stan(a)hardwarefreak.com> wrote:
> Arthur Machlas put forth on 7/28/2010 11:14 PM:
> In "make menuconfig":
> <snip>
> These last two are probably the reason for the "unknown", especially given
> you're running 2.6.34 which has all the CPU models currently on the market.

Probably just a problem with linuxinfo, which I'd never heard of
before, but installed when cpuinfo was not found and aptitude
suggested linuxinfo provided it. In any event, cat /proc/cpuinfo shows
all the right information.

You can't.. or rather, I can't select SMT support without first
checking SMP support.

> In "Power management and ACPI options"
> <snip>
> You'll have to figure out all the other menu config settings on your own, as
> most of us kernel monkeys have. ;)  These are simply the ones that directly
> relate to your questions.
>
> Hope this helped get you closer.

Somewhat. All those were pretty much done already. Greg KM's Kernel In
A Nutshell book is quite comprehensive and let me build an initrd-less
kernel in one try. Things are running nicely, but the problem I hoped
to resolve hasn't been. Namely, the lowest frequency my cpu can reach
is 1Ghz... instead of the 800Mhz that it reaches on windows and in the
spec sheets.

Advice on how to proceed from here is greatly appreciated.

Best,
AM


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From: Christian Jaeger on 29 Jul 2010 21:30
How do you read the possible cpu frequencies?

Your kernel needs cpufreq support and ondemand, powersave, etc.
governors; check with
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

Although with some hardware AFAIK other drivers than cpufreq are used,
I don't know for Atom.

Ch.


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From: Stan Hoeppner on 30 Jul 2010 02:00
Arthur Machlas put forth on 7/29/2010 12:01 PM:

> Things are running nicely, but the problem I hoped
> to resolve hasn't been. Namely, the lowest frequency my cpu can reach
> is 1Ghz... instead of the 800Mhz that it reaches on windows and in the
> spec sheets.
>
> Advice on how to proceed from here is greatly appreciated.

I led you to the well but it's up to you to drink Arthur. You didn't read the
help screens. All the frequency info you need is there. It is the key to you
succeeding at this. You may have to experiment some, but that's a requirement
when rolling one's own kernels. Welcome to the club. It's rarely "easy". ;)

BTW, I'm curious as to your motivations for this. Is this basically a
"Windows can do 800MHz, so $deity dammit, Linux should be able to do it as
well!" thing? In practical terms Arthur, you will not notice a meaningful
difference in thermal output or current draw (battery consumption) between
800MHz and 1GHz with the n450. The n450 has a TDP of 5.5 watts at 1.66GHz.
Thus you won't even save 1 watt going from 1GHz to 800MHz in power save mode.
It'll be something like 300 milliwatts or less. This exercise of yours is
futile if your goal is a _practical_ difference in system operation.

--
Stan


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