[Rtai] Source of big latencies???

Paolo Mantegazza mantegazza at aero.polimi.it
Wed Sep 28 15:17:11 CEST 2011


Federico Bergero wrote:
> The 82801JI (ICH10 Family) chipset is not listed in smi-module.c (I'm
> using rtai 3.8.1).
> I see that in the CVS is listed so now I'm going to try to compile
> magma from cvs.
> But anyway, I had added
> #ifndef PCI_DEVICE_ID_INTEL_82801JB_10
> #define PCI_DEVICE_ID_INTEL_82801JB_10 0x3a16
> #endif
> To the smi-module.c and I could installed it.
> The module told me
> 
> [  196.245964] RTAI: Intel chipset found, enabling SMI workaround.
> [  196.245977] SMI configuration has been cleared, mask used = 1
> (saved mask setting 1).

with that mask you have disable SMI completely, so the problem shopuld 
be elswhere. Try to work UP first.

paolo

> But still got those big latencies...
> 
> Do I have to run setsmi now? With what parameters?
> 
> 
> Thanks
> Fede
> 2011/9/28  <mantegazza at aero.polimi.it>:
>>> 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?
>>>
>> RTAI should find ICH10_1, anything greater is not set for a search in
>> smi_module.c
>>
>> paolo
>>
>>> 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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