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Subject[ARM64] Printing IRQ stack usage information
Hi All,

I have a requirement in printing irq stack usage information for each cpu.
I am using the following:
Linux Kernel: 4.9.x
Board: hikey620 (arm64, armv8 with 8 cores)
Platform: Ubuntu 14 debian

As a vague idea, I tried to implement like this:
-------------------------------------------------------------
static int dump_irq_stack_info(void)
{
int cpu, actual;
unsigned long irq_stack_ptr;
//unsigned long sp, sp1;
unsigned long stack_start;
unsigned long used;

actual = IRQ_STACK_SIZE;
used = 0;
pr_info("CPU UNUSED-STACK ACTUAL-STACK\n");
//seq_printf(m, "CPU UNUSED-STACK ACTUAL-STACK\n");
for_each_present_cpu(cpu) {
irq_stack_ptr = IRQ_STACK_PTR(cpu);
//sp1 = current_stack_pointer;
//sp = IRQ_STACK_TO_TASK_STACK(irq_stack_ptr);
stack_start = (unsigned long)per_cpu(irq_stack, cpu);
used = irq_stack_ptr - stack_start;
pr_info("%2d %10lu %10d\n", cpu, used, actual);
//seq_printf(m, "%2d %10lu %10d\n", cpu, used, actual);
}

return 0;
}
-------------------------------------------------------------
Currently, when I tested this (as a proc interface), I got the below output:
CPU UNUSED-STACK ACTUAL-STACK
0 16368 16384
1 16368 16384
2 16368 16384
3 16368 16384
4 16368 16384
5 16368 16384
6 16368 16384
7 16368 16384
-------------------------------------------------------------

But, I have some doubts:
1) I am not sure if my implementation is in right direction, or the
logic is totally wrong.
2) Is there better way to perform the similar objective?
3) How should I test it to get the different usage values for unused stack ?
Can I get these values by implementing a sample interrupt handler,
and printing information from there?

If this works, then I want to use it as part of dump_backtrace() function.

If anybody have done a similar thing in past, or have some ideas to
share, please help me.

Note: This is required only for our internal debugging purpose.


Regards,
Pintu

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