[Xenomai-help] Slow boot with Xenomai

[Xenomai-help] Slow boot with Xenomai

[Felipe Brandão Cavalcanti]

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Hello,
We are currently trying to install Xenomai (version 2.5rc2) on a Geode GX1
(PCM 3350 board), kernel 2.6.26 (Debian 5.0). However, we have run into a
few issues.

Whenever we install the kernel with Local APIC support enabled, xenomai
gives the error:

Xenomai: Local APIC absent or disabled!
Disable APIC support or pass "lapic=1" as bootparam.


Passing the lapic=1 parameter doesn't seem to do much, so we decided to turn
off APIC support in the kernel.

The kernel now boots, however, it does so extremely slowly. It is hanging
(i.e., takes a long time) whenever an IRQ probe is required.
The latencies are also pretty bad - worst case in xeno-test is 2ms!

So, any ideias on why this is happening?

Thanks for the help,
-- 
      -Felipe Brandão Cavalcanti
      LARA - Robotics and Automation Laboratory
      Department of Electrical Engineering
      UnB - University of Brasília, Brazil
      http://www.lara.unb.br/

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Re: [Xenomai-help] Slow boot with Xenomai

[Gilles Chanteperdrix]

Felipe Brandão Cavalcanti wrote:
> Hello,
> We are currently trying to install Xenomai (version 2.5rc2) on a Geode GX1
> (PCM 3350 board), kernel 2.6.26 (Debian 5.0).

The Geode is a very very bad choice:
- it is going to disappear any time soon
- its performances in many domains are far from the average x86
performances.

 However, we have run into a
> few issues.
> 
> Whenever we install the kernel with Local APIC support enabled, xenomai
> gives the error:
> 
> Xenomai: Local APIC absent or disabled!
> Disable APIC support or pass "lapic=1" as bootparam.

Ok. I guess your Geode does not have an APIC. I have a Geode and just
checked, it has the same issue, so, you should turn of apic in kernel
configuration. Maybe something is needed in the BIOS to enable it
(because the AMD specs say that the Geode has an APIC).

> 
> 
> Passing the lapic=1 parameter doesn't seem to do much, so we decided to turn
> off APIC support in the kernel.
> 
> The kernel now boots, however, it does so extremely slowly. It is hanging
> (i.e., takes a long time) whenever an IRQ probe is required.
> The latencies are also pretty bad - worst case in xeno-test is 2ms!
> 
> So, any ideias on why this is happening?

Probably an issue induced by power management disabling the tsc. So the
usual advices apply, please be sure to disable any smart power
management issue in the bios configuration and to boot with ACPI enabled
(except ACPI_PROCESSOR). Someone, a long time ago, posted on the RTAI
mailing list a way to disable this tsc thing by running an outb at a
well defined address, but I never was able to test it since my Geode
does not have this issue. Another workaround reported to work is to boot
with idle=poll passed on the command line. Yet another workaround is to
avoid using the tsc (by selecting in the kernel configuration a
processor without tsc), but this means a lot of overhead.

-- 
					    Gilles.

Re: [Xenomai-help] Slow boot with Xenomai

[Steven Seeger]

On Aug 6, 2009, at 4:32 PM, Gilles Chanteperdrix wrote:

> The Geode is a very very bad choice:
> - it is going to disappear any time soon
> - its performances in many domains are far from the average x86
> performances.

Agreed.

>
> Ok. I guess your Geode does not have an APIC. I have a Geode and just
> checked, it has the same issue, so, you should turn of apic in kernel
> configuration. Maybe something is needed in the BIOS to enable it
> (because the AMD specs say that the Geode has an APIC).

I've also tried to figure out how to get it to work with both a GX1  
and an LX-800 and cannot get it to work. I have read on other lists  
that there is no APIC.

> Probably an issue induced by power management disabling the tsc. So  
> the
> usual advices apply, please be sure to disable any smart power
> management issue in the bios configuration and to boot with ACPI  
> enabled
> (except ACPI_PROCESSOR). Someone, a long time ago, posted on the RTAI
> mailing list a way to disable this tsc thing by running an outb at a
> well defined address, but I never was able to test it since my Geode
> does not have this issue. Another workaround reported to work is to  
> boot
> with idle=poll passed on the command line. Yet another workaround is  
> to
> avoid using the tsc (by selecting in the kernel configuration a
> processor without tsc), but this means a lot of overhead.

We use TSC with idle=poll and things work correctly. However, the  
power saving mode will not run. However, gx1 is efficient and does not  
require a heatsink or fan, so it will not hurt your hardware. If you  
are running off a battery then you might want to use another approach.

The big issue with geode is the SMI overhead. It's terrible, and it  
will be a thorn in your side as you try to minimize jitter. I suggest  
you consider another board. Someday when I get some time, I may try  
and look into an smi disable function for geode. I think Gilles was  
going to look into it at some point, too. I've not really had a chance  
to work with Xenomai since May as the company I assist part time has  
been working on other things lately.

Steven