Am 20.04.2015 um 16:33 schrieb [email protected]:
Hi,
I am developing a UAV control system on the Beaglebone Black. I have tried
to use threads (infinate loops, so they run continuously) in my application
to send telemetry data from the plane, receive instructions from the
ground, control the plane and so on. I found that the threads run fine most
of the time, but once in a while there is a snag that occurs, which can
last up to 3 secs. This is very catastrophic for my orientation algorithm
as because it integrates gyro data over the small time scales it usually
takes per iteration.
I have found that when I run the code serially, the snags disappear
completely, but they return even when I introduce a thread that does
nothing (infinite loop with a sleep). This means that it has nothing to do
with threads accessing the same data simultaneously. It appears to be a
consequence of merely having threads.
I have used boost::threads as well as std::threads but they both have the
snag once every few seconds.
- The board I am using is the beaglebone black rev c
- I am running ubuntu 14.04
- The kernel is 3.8.13-bone68
I would really appreciate any help because I really need to be able to run
threads.
Threads are serialized by the OS, especially if there are more threads
than cores. If you now have a look at how many threads/processes are
running on your machine (e.g. by using "ps aux"), you might get an idea
how complicated that topic actually is, especially on a single core system.
To give a small hint:
Whenever your code enters a system call the OS might decide to give up
the remaining piece of the time slice reserved for the actual thread.
So it might be a good idea to enable preemption in the kernel, adjust
the timer frequency there and have a look at all the other knobs a Linux
system offers (e.g. sysctl -a), besides being aware of locking problems
and such in your own code. Not to mention problems with slow I/O (e.g.
swap on sd-cards).
Regards,
Alexander Holler
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