Re: BCM cyclic transmission tasks : cpu load

[Oliver Hartkopp <socketcan@hartkopp.net>]

Hi Maxime,

On 16.04.2015 19:28, Maxime Vinci wrote:
> This is my first message on a mailing list like this one, please be gentle ;)

Welcome. But beware - we are monsters :-)

> Currently, I am using the SocketCAN BCM feature to setup cyclic frame
> transmissions.
>
> Setting up everything appears to work fine : I can create multiple
> tasks with different periods, with one or more frames in each one.
>
> I would like to use it inside a Qt application (with qml based user
> interface), but it seems that right when I set up the first cyclic
> task, the cpu load increase from ~5% to 100%.
>
> Even when all tasks are deleted (by using the opcode TX_DELETE), the
> cpu load stays at the same level.
>
> To see if the UI was messing it up, I wrote a simple test program
> where I call the BCM functions to set up some cyclic tasks before
> entering a Qt application event loop (a simple "Hello world" app).
>
> It showed me that the cpu load goes crazy when the event loop starts.
>
> Correct me if I am wrong, but according to these 2 behaviors, it could
> be assumed that the issue happens every time the BCM and a Qt-based UI
> are being used together.
>
> Does anyone have any hints about this particular issue ?

I know about a colleague who's using Qt together with SocketCAN - but I'm not 
sure if he uses CAN_BCM sockets or only CAN_RAW. But AFAIK he implemented the 
communication stuff (including CAN access) into a separate thread.

So one suggestion would be to use strace (-> man strace) to check what's going 
on at syscall level. E.g. when your event loop does some blocking/polling 
stuff you can likely see it.

Regards,
Oliver

> PS: I did not try to put the object that wraps the BCM features in a
> new thread, but I think this will not solve the problem. (this is kind
> of done inside SocketCan, right ?)

Maybe you give it a try ;-)