[Rtai] Source of big latencies???

Federico Bergero fedebergero at gmail.com
Wed Sep 28 20:27:39 CEST 2011


I recompiled the kernel without SMP so Linux is using ONE core.
I still got those results.
I will continue to investigate, but without any clues where to start.
Is it posible that the smi modules is not turning off SMI? Can I tell
if SMI is actually disabled?

What else could be so periodic?

Thanks
Fede

2011/9/28 Paolo Mantegazza <mantegazza at aero.polimi.it>:
> 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.
>>>>
>>>
>>>
>>
>>
>>
>
>



-- 
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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