On 02.03.20 12:03, Bradley Valdenebro Peter (DC-AE/ESW52) via Xenomai wrote:
Hello Xenomai team,
We need you help understanding and solving a possible IRQ's off issue.
We are running a Xenomai/Linux setup on a Zynq Z-7020 SoC (We run Linux on CPU0
and Xenomai on CPU1):
- Linux version 4.4.0-xilinx (gcc version 8.3.0 (Buildroot
2019.02-00080-gc31d48e) ) #1 SMP PREEMPT
- ipipe ARM patch #8
- Xenomai 3.0.10
Lately we have been experiencing that our highest priority real time Xenomai
thread sort of halts for around 1ms every now and then.
After some investigation and tests we decided to enable ipipe trace to measure
IRQs-off times. See below the output of /proc/ipipe/trace/max
I-pipe worst-case tracing service on 4.4.0-xilinx/ipipe release #8
-------------------------------------------------------------
CPU: 0, Begin: 2944366216549 cycles, Trace Points: 2 (-10/+1), Length: 780 us
Calibrated minimum trace-point overhead: 0.288 us
+----- Hard IRQs ('|': locked)
|+-- Xenomai
||+- Linux ('*': domain stalled, '+': current, '#': current+stalled)
||| +---------- Delay flag ('+': > 1 us, '!': > 10 us)
||| | +- NMI noise ('N')
||| | |
Type User Val. Time Delay Function (Parent)
| +begin 0x80000001 -12 0.414 ipipe_stall_root+0x54 (<00000000>)
| #end 0x80000001 -11 0.822 ipipe_stall_root+0x8c (<00000000>)
| #begin 0x80000001 -11 0.414 ipipe_test_and_stall_root+0x5c
(<00000000>)
| #end 0x80000001 -10 1.095 ipipe_test_and_stall_root+0x98
(<00000000>)
| #begin 0x90000000 -9 0.665 __irq_svc+0x58 (arch_cpu_idle+0x0)
| #begin 0x00000025 -8 2.883 __ipipe_grab_irq+0x38 (<00000000>)
|#*[ 558] SampleI 49 -5 2.619 xnthread_resume+0x88 (<00000000>)
|#*[ 0] -<?>- -1 -3 2.052 ___xnsched_run+0xfc (<00000000>)
| #end 0x00000025 -1 0.760 __ipipe_grab_irq+0x7c (<00000000>)
| #end 0x90000000 0 0.530 __ipipe_fast_svc_irq_exit+0x1c
(arch_cpu_idle+0x0)
| #begin 0x80000000 0! 780.110 arch_cpu_idle+0x9c (<00000000>)
<| +end 0x80000000 780 0.570 ipipe_unstall_root+0x64 (<00000000>)
| +begin 0x90000000 780 0.000 __irq_svc+0x58
(ipipe_unstall_root+0x68)
Looks like the CPU was idle and received no IRQ during that time. Is
some power management active? Is some timer misprogrammed? Or where
should the next interrupt have from?
We have trouble understanding the output but we can see a max length of 780us
on CPU0. We find this value extremely high.
With our current requirements anything beyond 10us is not acceptable.
780 us is definitely off on that target, but 10 us will likely be too
ambitious as well. Maybe, maybe, with well configured strict core
isolation, practically no Linux load on the RT core and your critical RT
code path always in cache... But I would consider that highly risky,
given this low-end CPU on that target SoC.
Jan
Can someone with experience with the ipipe tracer please help us understand
what is going on and how can we fix it?
Thanks in advance for your support.
Best regards.
Peter Bradley
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
