Re: More details on health monitoring notifications

[Philippe Gerum <rpm@xenomai.org>]

Russell Johnson <russell.johnson@kratosdefense.com> writes:

> [[S/MIME Signed Part:Undecided]]
> I also notice these lines in “dmesg” output from the EVL core. Can I use the excpt or user_pc to get any more information about what is causing these in-band switches?
>

Yes. Exception #14 on x86 is 'page fault' event, which seems to be the
architecture this code is running on. User_pc is the PC value in the
virtual address space of the process when it causes the trap in this
case. This is a - possibly legit - memory access which requires a
so-called 'major fault' to be taken.

GDB may help figuring out the location of this code, in two ways:

- switching the HM notifier to 'signal' mode for your threads, using
  T_HMSIG, you only need to run the app over GDB: the core will send it
  a SIGDEBUG event, which GDB will trap. Using the GDB 'backtrace/bt'
  command once the app is in break state after receipt should display a
  backtrace to the offending code (IOW the EVL core makes sure that your
  app receives SIGDEBUG immediately on top of the code causing the
  trap).

- using the GDB 'list' command to list the code at the PC value reported
  by the kernel should work. You just need to start the application
  first: unless you have a complex dlopen-based scheme for running code
  plugins, running until a breakpoint is taken in main() should be
  enough before you can issue 'list *<PC_value>'.

>  
>
> [ 7301.352255] EVL: thread_1 switching in-band [pid=6319, excpt=14, user_pc=0x7f54a7877fa6]
>
> [ 7301.352689] EVL: thread_2 switching in-band [pid=6285, excpt=14, user_pc=0x7f54a7877fa6]
>
>  
>
> From: Russell Johnson 
> Sent: Friday, July 1, 2022 11:19 AM
> To: xenomai@lists.linux.dev
> Subject: More details on health monitoring notifications
>
>  
>
> Hello,
>
>  
>
> I have gotten a health monitoring thread going that tracks all the EVL threads running in my app. The goal was to try and figure out what is causing occasional in-band switches in some of my EVL threads. I am seeing the notifications now that give me a little more insight, and the two diagnostic codes I am seeing are 2 (switched inband due to syscall) and 3 (switched inband due to fault). I am finding these to be quite hard to pinpoint
> specifically throughout my code. Is there any way to get more information into what exactly is causing these notifications from the EVL core? It would be great to have a callstack of some kind, but I am not sure if that is possible. Any insight would be helpful.
>
>  
>
> Thanks,
>
>  
>
> Russell
>
> [[End of S/MIME Signed Part]]


-- 
Philippe.