Real time delay issue

Hi

I'm currently working at full time in this machine:



I run 2 "glxgears" and at the same time make a copy of a large file (almost 8Gb), move windows around and this are the results:




I had already open another thread with my problem, can see it there:

www.linuxcnc.org/index.php/english/forum...cted-real-time-delay

when I start linuxcnc after a few seconds I got one error, "unexpected real time delay". the linuxcnc version is 2.5.1 installed on a Asrock AD2700B-ITX with a 60Gb SSD. it uses the mesa 5i20 + 7i37+7i33+7i44+7i73 but at the moment only mesa 7i73 is connected to the panel, the other boards haven't any encoders or motors attached.



I erase the old configuration and run a pncconf to make a new configuration. don't solve the problem. I have more than one month of working on this machine and it's kind of demotivating can't solve this problem when the machine starts to get shape.

Tanks

João

What have you tried so far to try to improve the latency results?

Have you turned off things like hyperthreading and anything to do with power management in the bios?

Did you set up isocpu?

What speed do you have the servothread set at? (these atom cpus are not the fastest of racehorses anthing much faster than about 500000 is probably not practical)

What are you using for your video driver?

Hi

Have you seen these FAQs?
www.linuxcnc.org/index.php/english/forum...-the-latency-problem
www.linuxcnc.org/index.php/english/forum...me-latency-solutions

As Todd says these dual core Atoms usually give better latency with isolcpus=1 kernel parameter, hyperthreading off if in BIOS and all BIOS power management stuff turned off, fan set to constant speed ( if available).

They also have a built in video chipset that has no open source driver on a lot of the 2700 / 2800 boards, the vesa driver works OK with it up to 1024x768, check what your install is using.

Run the latency test described in the FAQs from the /usr/src/realtime-xxxx/testsuite/

This will show when the spike is occurring and if it recurs.
You can also look at it when doing heavy graphics stuff, openGL stuff, disc access, network access, to try to narrow down the cause.

Several boards have been tested, some by PCW I believe, that have initial high spikes and then nothing worth mentioning thereafter.

Looking at the size of the machine and the fact that you are using Mesa boards, I am guessing it is servo powered.
Base thread latency becomes less important on systems that do not use steppers and software step generation, so all is far from doom at present.

regards

Hi

yes I turned off almost anything on the bios. I don't find any isocpu option on the bios.

for the video driver, when I do "lspci" shows this:

00:02.0 VGA compatible controller: Intel Corporation Device 0be2 (rev 09)

I tested with 1000000ns using the SVST4_8 firmware on mesa 5i20, got this error one time in six or seven times that run linuxcnc, but I have to use
SVSS4_8 firmware because the pendent board, with 1000000ns I get the error many times. If I set the time to 1500000ns I run linuxcnc several times don't show any errors. but I have no idea if it is a acceptable amount of time. the machine uses 3 servos.

I don't find any isocpu option on the bios.

It is a kernel parameter not a BIOS option
see
wiki.linuxcnc.org/cgi-bin/wiki.pl?Troubl...lcpus_Boot_parameter

00:02.0 VGA compatible controller: Intel Corporation Device 0be2 (rev 09)

Yeah thats the bugger, you may have to try
xf86-video-vesa
or
xf86-video-fbdev driver

EDIT its just called vesa in Ubuntu

(If you do lspci -vv it will show which driver is in use)

If you ever got a real time error at a 1 KHz servo thread this means in some circumstance you have more than 200 usec of latency. This simply should not happen. This is a BIOS/Motherboard issue.

The fact that this happens more often with different firmware is probably not important, as I can run either firmware error free with a 4 KHz servo thread.

If you haven't figured it out yet, this wiki page has pretty good instructions how to impliment the isolcpus function.

wiki.linuxcnc.org/cgi-bin/wiki.pl?The_Is..._Parameter_And_GRUB2

Doing this on my D2700 took my latecy from somthing simular to yours down to about 9000. Now I only get an occasional real time error, mostly because I am trying to run my servo thread a little to fast (torque mode servos)

tanks for the comments. I will try to install vesa drivers and configure the isolcpus function.

João

I would do the isolcpus first, see what happens and then if there is still a problem look at the video driver.

The tip about the isolcpus solved the issue (at least for now, as we did not get any more issues in 2 days).