ubuntu10.04 Lcnc 2.7 rtai error

I believe that you are seeing a caching issue

My experience with Preempt-RT and our Ethernet cards show the same thing,
the faster you set the servo thread, the faster you _can_ set the servo thread
because the LRU cache algorithm keeps the main RT parts cached if they are
accessed frequently enough

I have also noticed that CPUs with larger caches have better RTAI and Preempt-RT performance
Here's a fast CPU with a 3M cache:

Preempt-RT
freeby.mesanet.com/h97-g3258-preemt-rt.png

RTAI
freeby.mesanet.com/g3258-rtai.png

@ ArkEyes .. for experience I try to run latency with arguments ....

@PCW ... than if try the same config with asrock Q1900B-itx (intel 4 core 2M chache) I've the better result ...

My problem at the end si that .... as suggest PCW I try halscope ... noew with 2 channel fo encoder ... but not see nothings eccepts the 2 signal .... 8000 samples at 1Khz .... Wicth is the command to run halscope at 10Khz for example??... I can change by hand the value of jogwheel encoder!

Anyhow ... the realtime issue is show in axis (in touchy too??) and if the error is not a real problem how do you disable the error message so that it is never seen ?

Regards
Giorgio

latency-test 1ms from my 17:45 (forum hour) to now (surfing, 3 youtube windows): servo thread 1ms Max Jitter 38404 .... and no go up if run some other program ....

After 16 hour of youtube html5 and flash player videos, running bash script for open and close a program .... latency-test 1ms = 44932 ....

Tonight I've a doubt .... than today i've create a config with stepconf and parallel port ..... I make a bash for launch and close it (100 time) ... never see the realtime error ..... than try to launch mymachineconf (with mesa 5i25 + 7i77) at 2° time have the error 5/6 sec after the launch .....

that means something ?

Regards
giorgio

It means that the 1 MS thread has experienced >200 usec delays occasionally
It may be that you dont have real time errors in the parallel port case because the base
thread keeps the cache filled with RT code.

On poor RT hardware (and I consider all Atoms up to Baytrail quite poor)
You might try ArcEyes trick of running a dummy base thread


I might note that I do not see any RT errors on my D510 running a 1 KHz thread
(and its run Mesa hardware continuously for years at a time)
It might be related to the Power VR graphics in the CedarView (D2xxx) series Atoms

@PCW --- your suggestion at last is buy a motherboard with cpu with more cache and greater frequecy .... Is right? You can suggest an quite good cpu and motherboard? (consider my choice for now is ubuntu 10.04 .... with debian before we have to play a little longer and completely skip wheezy )

if that's what you suggest seems the lesser evil. I'll wait for your confirmation.

Regards
giorgio

@ arkEye or @PCW is possible that the problem (rtai error on start up only with mesa5i25) is become from buffered RAM. My ram isn't buffered but in asrock j1900-itx not work (crucial ddr3 ram as ad2550b motherboard) ... I've read some post where someone suggest not use crucial ddr3 because it has some kind of buffer anyhow ....

Not likely this is RAM related at all

Do you have issues with the J1900 or just the D2550?

The J1900 have a wrong ram because not start at all.

Instead I try with H97M gigabyte and I3 3Ghz 4° gen.
All ok .... whit any type of trik on rtai and cpu, withous disable sometings from bios, whit 6 glgears whindows and 2 firefox youtube open after 2 hour obtain

servo thread 1ms 10580

base thread 25usec 11900

I think if I block 1 CPU for linuxcnc an disable any things from bios all system work perfectly .

No see at all rtai error message. ..... Ubuntu 10.04 linuxcnc 2.7

regards
giorgio

IMHO

I would toss out Ubuntu 10.04 as its no longer maintained and use Wheezy

I would not bother with isolcpus at all as it will just slow the system down to gain a few usec better latency

With hardware stepgens and servo systems, any latency in the 0 to 50 usec range is absolutely fine,
there is really no point in getting better (and up to 500 usec can be OK with the right hardware setup)