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Old 07-29-2010, 04:14 AM
Arthur Machlas
 
Default Intel Atom N450 & Kernel Config Options SMP

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@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@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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Old 07-29-2010, 10:46 AM
Stan Hoeppner
 
Default Intel Atom N450 & Kernel Config Options SMP

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@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@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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Old 07-29-2010, 05:01 PM
Arthur Machlas
 
Default Intel Atom N450 & Kernel Config Options SMP

On Thu, Jul 29, 2010 at 5:46 AM, Stan Hoeppner <stan@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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Old 07-30-2010, 01:20 AM
Christian Jaeger
 
Default Intel Atom N450 & Kernel Config Options SMP

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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Old 07-30-2010, 05:52 AM
Stan Hoeppner
 
Default Intel Atom N450 & Kernel Config Options SMP

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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Old 07-30-2010, 02:04 PM
Arthur Machlas
 
Default Intel Atom N450 & Kernel Config Options SMP

On Fri, Jul 30, 2010 at 12:52 AM, Stan Hoeppner <stan@hardwarefreak.com> wrote:
> 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".
>
Asking on here isn't my first attempt at figuring things out. My
kernel config work is based on Greg KM's book "The Linux Kernel In A
Nutshell". So, not only have I read the help screens, but I've also
read a pretty decent book by one of the kernel's prime maintainers.

I should have been more clear about the advice I was hoping for, since
there is nothing wrong with my kernel config, I was looking for advice
about how to go about further debugging this issue of not having full
frequency range. I wanted to give fixing it a solid try before filing
a bug against the kernel itself.

> 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?

Not as such. More like a my processor is supposed to scale from 800Mhz
to 1.6Ghz, and its strange that it doesn't. I wonder why.

> 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.

I suppose that will have to count as advice on how to proceed, but I
hope you'll forgive me if I continue to search for an answer. Your
comments are reassuring to me though, that it isn't a serious problem,
and I do thank you for that.

At this point, I'm thinking it's a problem with the kernel or a
problem with my bios, and I think there are some kernel command line
parameters I can use to test the latter in Greg's book.

Best wishes,
AM


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Old 07-30-2010, 02:50 PM
Arthur Machlas
 
Default Intel Atom N450 & Kernel Config Options SMP

On Thu, Jul 29, 2010 at 8:20 PM, Christian Jaeger <chrjae@gmail.com> wrote:
> 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.
>

Hi Chris,

Available frequencies are taken from
/sys/devices/system/cpu/cpu0/freq/available_scaling_frequencies, in
addition powertop shows the same information.

Governors are all compiled into the kernel, and switching between them
by echoing "conservative" or "ondemand" to
/sys/devices/system/cpu/cpu0/freq/current_scaling_governor works. I
haven't tried user space yet, because I don't have any userspace tools
installed right now to change cpufreq. I'll remedy that this weekend
and see if it makes any difference.

Currently I'm using the acpi_cpufreq built into the kernel, however a
few other intel related ones like p4 and even those marked as
deprecated are built as modules.

Appreciate the input,
AM


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Old 07-30-2010, 04:27 PM
Stan Hoeppner
 
Default Intel Atom N450 & Kernel Config Options SMP

Arthur Machlas put forth on 7/30/2010 9:04 AM:

>> 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?
>
> Not as such. More like a my processor is supposed to scale from 800Mhz
> to 1.6Ghz, and its strange that it doesn't. I wonder why.

That's what I figured. I had a similar mindset when I was a younger man. Let
me share a relevant story:

Back in 1997 I bought a beautiful used Midnight Blue 1993 Ford Probe GT with
the hopped up 24 valve quad cam V6 and a 5 speed manual transmission. It was
Motor Trend Magazine's 1993 Car Of The Year. The tested top speed was 137
miles per hour. I was dead set on achieving that published top speed. I
didn't have a racetrack available for my testing. Over the course of about 3
weeks I would find open stretches of Interstate 370 with little to no traffic.
On 5 occasions I was able to hit 135 mph, but no more. I was determined to
hit the magical 137 that Motor Trend said it would do. On the six occasion on
a cool afternoon I had just hit 136 mph when I rocketed past a hidden Missouri
Highway Patrolman manning a radar gun. As soon as I saw the cherries in my
rear view mirror I slowed down and pulled over. Evading wasn't an option even
with that kind of speed and lead: you can't outrun a radio or a helicopter.

Due to traveling at almost double the posted speed limit I spent a mandatory
night in jail. The attorney cost me $450 and the ticket for doing 76 mph
_over_ the posted speed limit was $548, for a grand total of $998. The
attorney got the reckless driving charge dropped and massaged the speeding
charge so I only took a 2 point hit on my license instead of 5. A reckless
driving conviction along with the additional points would have put me into
what the insurance industry calls the "high risk" category, which would have
quadrupled my insurance premiums. That would have driven my monthly insurance
payment to just under $500/month, which was more than my split of rent at the
time.

The moral of the story: Even if "they" say it will do it, and others have
achieved it, it's not always wise, nor cost effective, to maniacally chase the
numbers.

> I suppose that will have to count as advice on how to proceed, but I
> hope you'll forgive me if I continue to search for an answer. Your
> comments are reassuring to me though, that it isn't a serious problem,
> and I do thank you for that.

There's nothing to forgive. It's your time and effort going into this. I'm
simply trying to save you large amounts of both as I've "been there and done
that".

> At this point, I'm thinking it's a problem with the kernel or a
> problem with my bios, and I think there are some kernel command line
> parameters I can use to test the latter in Greg's book.

And before filing a kernel bug, it would be very wise to ask the questions you
have here on lkml before you submit a bug. Debian-users isn't really the
proper venue for discussing your problem. This is a user list, not a
developer list. There are very few, if any, kernel hackers on this list with
the knowledge/answers you are seeking. And no I'm not one of them. Having
more than cursory experience rolling my own kernels is a far cry from being a
kernel hacker. I'm not a C programmer.

My advice: expend your energy on aspects of Debian/Linux that will yield
practical, tangible benefits. This isn't one of them.

--
Stan


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