On 06/10/2017 01:13 PM, rolf.freitag@xxxxxxxx wrote:
Hi, I tried ping as a minimal latency test, e. g. ionice -c3 -p $$ renice +19 -p $$ ping -q -s 28 -l 1 -p 0f1e2d3c4b5a6978 -i 0.001 localhost but when cyclictest shows a worst-case latency of 40 mikroseconds, ping shows more than 10,000 (after 1 day run). I tried different kernels, e. g. SMP PREEMPT RT Debian 4.6.4-1~bpo8+1 (2016-08-11) x86_64 but with the same result, low cyclictest values, high ping values. What is the reason?
Since no one else has answered, I guess I will. Creating a real-time *system* is hard work. Just running a program on a real-time OS does not magically make it a real-time system. You really have to know what you are doing. I suggest you read "POSIX.4 Programmers Guide: Programming for the Real World" for an intro to the subject. It's fairly close to what Linux does, though there are things that Linux does beyond what is in there. A few notes on what you have done: * ionice doesn't affect network I/O. * renice does not set real-time priorities. * You don't do anything with memory locking. What happens if memory in your program gets paged out then is required? * Something on the other end of the ping is running, too. It also needs to be real-time, too, and it's not by default. I'd suggest you need to spend some time learning before you attempt something like this. -corey -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html