latency-test fine but axis complains

Hi all,

I keep getting axis complaining about delays while saying to run latency-test.

However, latency-test seems to run fine. I'm getting numbers about 18000ns while stressing it by a) compiling kernels, b) tarbzipping sources, c) copying large files from/to different partitions and pinging network card ip address, all at same time. Top reports average loads about 2.50 or more.

So, by latency-test results, system should work fine, but... axis still complains.

Is there something I could do or should I look for another system ?

Regards,

I'm getting numbers about 18000ns while stressing it by a) compiling kernels, b) tarbzipping sources, c) copying large files from/to different partitions and pinging network card ip address,

That is quite high considering you are doing nothing that touches the graphics system.

Trying running 5 instances of glxgears, open a youtube movie in firefox, alt tab between programs and move windows around with the mouse
Then what result do you get?

Often when Axis starts with a realtime error immediately, it is the sudden demands of rendering the plot of a program, plus the creation of the gtk window etc ie graphics related

This can sometimes be simply resolved if you are using on-board graphics, by inserting a graphics card.

A good one for AGP slot computers is a Matrox G550, I just bought 2 for £12 and they cured high latency on video events instantly on 2 P4s with integrated graphics that I had upgraded

I think they did a PCI version too, they are dirt cheap, scrapped from old machines on Ebay and just use a common source mga driver

regards

Hi,

I think you are right about the graphics subsystem being the source of overruns.

However, I'm not using an integrated card but an ATI AGP 4X with 64MB RAM. I understand that RAM is not the only thing to care about, but could you say which are the important things to care about when purchasing a graphics card intended to be used with linuxcnc?. I really appreciate your advice about matrox cards but I see they are very low in www.free3d.org/ ranking.

Yesterday I made my firsts chips and system seems to work fine... No errors reported; I tghink I could work with an interface without permanent backplot, or perhaps will buy another graphics card. This P4 -1.5 MHz gives (much) better numbers than my Athlon 64X2 so I hope it can be my CNC system for some years...

Regards

Hi

I think you are right about the graphics subsystem being the source of overruns.
......
I really appreciate your advice about matrox cards but I see they are very low in www.free3d.org/ ranking.

That is a list for gamers to b**t their m**t over,

I tghink I could work with an interface without permanent backplot

If you would contemplate running without a backplot at all, why would you baulk at fitting a low power graphics card that works.

ATI are second only to nVidia in terms of the problems caused regards latency. Between the two of them they dominate the market, which does not help.

Do a lspci -vv in a terminal and look at which driver is loaded for your graphics card
They will most likely be the non-free proprietary ones

If so try changing the driver for the opensource one (probably just called ati or radeon, but I don't know exactly which card you have)
this link may help
askubuntu.com/questions/8019/how-can-i-e...-open-source-drivers

regards

OK, I understand.

I'm ordering one of these matrox cards just now. Maybe I don't need it, but just in case it happens... and they are really dirty cheap.

Regards

Do try the opensource drivers as well and see how it goes.

nVidia in particular have an implementation of GLX in their proprietary drivers which causes lots of problems, not just with Linuxcnc, but with many other
applications making heavy use it

Don't know specifically about ATI, but there are enough problems posted on various forums to suggest it is worth a try

regards

Hi,

I'm using the radeon driver. Both nvidia and ATI propietary drivers gave me always a lot of problems with rt-preempt patch, so I almost never used them and I'm not planning to do it now.

About running glxgears, I tried it. I ran 12 instances of glxgears and got figures about 28000 ns max jitter, with no Internet browsing nor palying videos-music.

Regards

Both nvidia and ATI propietary drivers gave me always a lot of problems with rt-preempt patch

Are you using a rt-preempt kernel with Linuxcnc?

I have a partition with the Debian 7.1 rt-preempt kernel set up, but it always gives realtime errors and far worse latency than rtai

regards

'I'm using RTAI.

I mentioned rt-preempt because I used to compile rt-preempt for realtime audio work. nvidia and ati propietary drivers normally had to be patched to work with rt-preempt and this was not always possible, nor convenient, nor really functional, so there is a long time since I dropped that propietary drivers, and never buy any nvidia card.

On realtime audio work, 5 miliseconds latency could be "good enough" but a good target would be to have a 1-milisecond latency. As I understand it, my servo thread is a 1-milisecond thread too.

1-milisecond latency is doable with rt-preempt with the right hardware after you set thread priority conveniently. It has to be tuned by hand after installation. One could get some overruns then and now, normally while applications are starting. We already recorded some music bands and it works OK, final CDs have no latency issues at all.

About the base thread, wich seems to be much more exigent, I don't know if it would be possible with rt-preempt right now. I guess step generation would be worse that RTAI's and that's the important matter after all, so I'll work with RTAI.

"apt-get install linuxcnc" would be really nice, however.

Regards,