[Rtai] Source of big latencies???

Federico Bergero fedebergero at gmail.com
Tue Sep 27 19:51:03 CEST 2011


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.
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