IRQ's off issue
Bradley Valdenebro Peter (DC-AE/ESW52)
Peter.BradleyValdenebro at boschrexroth.nl
Mon Mar 2 14:09:09 CET 2020
Thanks for your fast response.
Power management is not active but if the ipipe trace IRQ's off shows the maximum time without an interrupt the value 780us might be alright.
We are currently running our highest priority real time Xenomai thread with a period of 1ms.
If we change the thread to a period of 125us we can see the value of the ipipe tracing dropping to 115us.
We were under the assumption that the ipipe trace IRQ's off shows the longest time interrupts have been disabled and not the longest time without an interrupt.
Is this assumption incorrect?
From: Jan Kiszka <jan.kiszka at siemens.com>
Sent: 02 March 2020 13:45
To: Bradley Valdenebro Peter (DC-AE/ESW52) <Peter.BradleyValdenebro at boschrexroth.nl>; xenomai at xenomai.org
Subject: Re: IRQ's off issue
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.
> 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
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