Tom, Am 20.02.2013 um 20:29 schrieb Tom Easterday:
> I have a problem that looks like either process scheduling, or buffering, > some sort of blocking on a linuxcnc host running 12.04/Xenomai and 2.6.0pre. > It does not display this problem on 10.04/RTAI and 2.6.0pre (same base > hardware, an intel atom board). The symptom is that when continuously > jogging, a DRO showing position on a remote device changes smoothly when > talking to 10.04/rtai. On 12.04/xenomai we get a distinct pattern of three > updates and a pause, three updates and a pause. The pause is some number of > milliseconds long (1/4 second maybe) and distinctly visible. The remote > connection is through our web server (Rockhopper) over tcp (websocket) on > wired ethernet. > > We first thought it was packet buffering or network latency and played with > TCP parameters and system buffers but that had no effect. We put timing > statements in the web server code at the point were we write the data out and > it appears that the whole web server process is being blocked or something. > We tried re-nicing the web server but it didn't help. If we run Axis locally > while doing this it doesn't display this pause, it moves along smoothly as > one would expect. > > For debugging I thought I might try 12.04 and rtai to see if it was just with > the xenomai kernel or if rtai on 12 does it as well. Are there rtai packages > available for 12.04 yet? I was going through the email list archive on the > new RT stuff but don't see any pointer to packages on rtai specifically... > > Any thoughts on what we might look at to narrow it down further? >From the above I can tell: - you are running some of your own code because you cite some 'web server' which is not part of a released or working branch. Where is the code, the configuration you are using, and the exact sequence of commands leading up to it? - you say you are running '2.6.0pre', whatever that is, that tag isnt a unique identifier. Please state repository, branch name, commit, and which changes you did. - you do not say anything about hardware, exact lan setup including any intermediate hardware, the board, kernel version - how are we supposed to guess? With that level of information, my thought is that you will get zero help in narrowing down things further, simply because it is impossible. -- that said, what I suggest you do is: triage the problem into a) network driver and hardware b) tcp kernel stack and throughput c) application. a) Find throughput tests which measure at the packet loss level with the least kernel intervention, that is - raw throughput tests at the ethernet or UDP level. Find out if there are significant differences between operating systems on the same hardware. Change hubs/switches or whatever have in between. Try a crossover cable. b) do the same including the TCP stack which measures end-to-end throughput at the TCP level. Observe the TCP retransmission numbers in netstat which should give a clue. c) as for application level issues, install wireshark and pcap, and trace the flow between the programs which show the the issue - we dont know which they are since you do not tell. The packet capture will include timestamps and TCP retransmissions which hint at network problems. If you see any retransmissions, try alternate hardware and drivers - this zoo has many animals. Try with everyting on one machine to exclude network issues. And: read this: http://www.chiark.greenend.org.uk/~sgtatham/bugs.html -- One reason why I suggest you produce a more thorough report, and not some ephemeral problem narrative: I spent several hours recently in a off-list debugging session on a 'reported Xenomai problem'. The problem was finally resolved by me demanding to 'yank that ethernet hub *now* and throw it in the wastebin' in no uncertain words. No more Xenomai issues since. Btw that was a device 'which always used to work so far'. So much for perceived causality. - Micahel ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_feb _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
