[Rtai] Source of big latencies???

Federico Bergero fedebergero at gmail.com
Tue Sep 27 22:07:34 CEST 2011


I have added the following lines
#ifndef PCI_DEVICE_ID_INTEL_82801JB_10
#define PCI_DEVICE_ID_INTEL_82801JB_10 0x3a16
#endif

And added PCI_DEVICE_ID_INTEL_82801JB_10 to the list.

to smi-module.c.

Now the module gets installed. I get
[  196.245964] RTAI: Intel chipset found, enabling SMI workaround.
[  196.245977] SMI configuration has been cleared, mask used = 1
(saved mask setting 1).

But I still got those 2.34 sec big latencies.

I'm not sure I that 0x3a16 is the correct device. 0x3a16 It is my
ISA bridge: Intel Corporation 82801JIR (ICH10R) LPC Interface Controller

Any thouths?


2011/9/27 Federico Bergero <fedebergero at gmail.com>:
> If it is of any help here's my lspci/dmesg.
>
> I see there a
> SMBus: Intel Corporation 82801JI (ICH10 Family) SMBus Controller
>
> But I still get the Intel chipset not found
>
> Any ideas?
>
> 2011/9/27 Federico Bergero <fedebergero at gmail.com>:
>> Sorry, I didn't follow you Paolo.
>> I should disable ACPI from the BIOS or recompile the kernel without
>> ACPI support?
>> I didn't understand neither what you said about SMI.
>> When I install the module I get:
>> insmod: error inserting './rtai_smi.ko': -1 No such device
>> RTAI: Intel chipset not found.
>>
>> How can I know 1) if I have a intel chipset 2) If I don't have one, I
>> need to do something else?
>>
>> Thanks in advance!
>> Fede
>>
>> 2011/9/27 Paolo Mantegazza <mantegazza at aero.polimi.it>:
>>> Federico Bergero wrote:
>>>>
>>>> Ok. I'll try setting only one core without HT in the bios.
>>>> That way Linux will only use one core.
>>>>
>>>
>>> I think there is no such a need, you have just to disable SMO on your
>>> system. A few times I've seen that just diabling ACPI set the PC UP.
>>> If you are using an INTEL chipset than the missing of it is likely related
>>> to the fact that SMI disabling RTAI need to have it listed.
>>>
>>> paolo
>>>
>>>> Anyway I'm using LXRT so I'm not using the UP nor the SMP (nor the
>>>> MUP) scheduler,right?.
>>>>
>>>> I tried taking care of SMI but when I insert the module it tells me
>>>> "No intel chip detected", so I thought that didn't need to do
>>>> anything. Is this correct? Or I have to do something anyway?
>>>>
>>>> I'll reply later with the new results
>>>>
>>>> Thanks
>>>>
>>>> Fede
>>>>
>>>> 2011/9/27 Paolo Mantegazza <mantegazza at aero.polimi.it>:
>>>>>
>>>>> Federico Bergero wrote:
>>>>>>
>>>>>> What do you mean by uni-processor?
>>>>>> I have disabled HT but still got 6 cores (a small SMP system).
>>>>>> Anyway the test fails with only one thread, so I don't think that HT
>>>>>> or multiple cores have anything to do with it.
>>>>>> In theory RTAI shouldn't give the processor back to Linux if the RTAI
>>>>>> task is doing something (like in a busy wait), right? If so, what
>>>>>> could have HIGHER priority than RTAI task? Bios? ACPI/APM?
>>>>>>
>>>>> To play with the config you should first configure Linux as UP. If the
>>>>> latency remains than you have to know what hardware you bought. If it
>>>>> does
>>>>> not than you have a clue related to what your hardware does SMP. Have
>>>>> cared
>>>>> of SMI already?
>>>>> Please keep posting to the list.
>>>>>
>>>>>
>>>>> paolo
>>>>>
>>>>>> Grazie tante!
>>>>>> Fede
>>>>>>
>>>>>> 2011/9/27 Paolo Mantegazza <mantegazza at aero.polimi.it>:
>>>>>>>
>>>>>>> Federico Bergero wrote:
>>>>>>>>
>>>>>>>> I have disabled HT in the BIOS (now running with 6cores)
>>>>>>>> I'm still getting a source of high latencies.
>>>>>>>> I found out that these big latencies are PERIODIC (?)
>>>>>>>> They occur every 2.43 seg.
>>>>>>>> I'm attaching the test I have run.
>>>>>>>>
>>>>>>>> I'm using the kernel from
>>>>>>>> http://hart.sourceforge.net/rtai_installation_10_04.html
>>>>>>>>
>>>>>>>> Any ideas what could be going on?
>>>>>>>>
>>>>>>> Have you tried the latency test after making your machine as if it was
>>>>>>> UP.
>>>>>>>
>>>>>>> paolo
>>>>>>>
>>>>>>>
>>>>>>>> These is the output of the test:
>>>>>>>> [   58.336000] Error diff 2343675702
>>>>>>>> [   58.336000] Error diff 2343677010
>>>>>>>> [   59.628000] Error diff 2343704223
>>>>>>>>
>>>>>>>> 2011/9/26 Paolo Mantegazza <mantegazza at aero.polimi.it>:
>>>>>>>>>
>>>>>>>>> Federico Bergero wrote:
>>>>>>>>>>
>>>>>>>>>> Hi I'm working on a project with rtai.
>>>>>>>>>> I'm using a Intel i7 with 6 cores and HT so Linux sees 12 cores.
>>>>>>>>>> I'm running a real time LXRT-RTAI thread on each core (indicating
>>>>>>>>>> RTAI
>>>>>>>>>> to do so with the cpus_allowed mask).
>>>>>>>>>>
>>>>>>>>>> Each thread runs a simulation of a system syncrhonized with real
>>>>>>>>>> time,
>>>>>>>>>> and I'm using rt_sleep/rt_busy_sleep to do the waits.
>>>>>>>>>> When running the simulation SOMETIMES I get a max latencies of 900us
>>>>>>>>>> on some processor and 2us on others processors.
>>>>>>>>>> These BIG latencies occur randomly. Sometimes everything runs
>>>>>>>>>> smoothly.
>>>>>>>>>> What could be the source of these lantencies? I have turned off Freq
>>>>>>>>>> Scaling in Linux and SpeedStep in the BIOS.
>>>>>>>>>>
>>>>>>>>>> Also I don't quiet understand how the rt_get_cpu_time_ns() is
>>>>>>>>>> implemented on a SMP system, could someone explain me this?
>>>>>>>>>>
>>>>>>>>>> Thanks Fede
>>>>>>>>>>
>>>>>>>>> First of all do not use HT.
>>>>>>>>> On your machine rt_get_cpu_time_ns() simply reads and converts the
>>>>>>>>> APIC
>>>>>>>>> timer on each CPU. You can check if their are big difference intra
>>>>>>>>> CPUs
>>>>>>>>> by
>>>>>>>>> configuring RTAI to do so.
>>>>>>>>>
>>>>>>>>> paolo
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> paolo
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>>
>> --
>> I find television very educational. Every time someone switches it on,
>> I go into another room and read a good book.
>>
>
>
>
> --
> I find television very educational. Every time someone switches it on,
> I go into another room and read a good book.
>



-- 
I find television very educational. Every time someone switches it on,
I go into another room and read a good book.


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