How many Interrupts at the same time?
Hi,
we have a custom made 403 based board with up to 128 interrupts which may occur simultaniously. After reading the interrupt handling code, we came to the
conclusion that when too many interrupts are stacked, the kernel stack will overflow.
When the first interrupt is handled the kernel leaves do_IRQ and returns to the assembly code
in entry.S where in do_soft_irq() the interrupts are reenabled due to issuing sti(). When
EE in the MSR is enabled the system will execute the next exception and store another sizeof
(struct pt_regs) bytes on the stack plus some additional data (stackframe, link reg., etc.).
This sums up to 184 bytes each. This leaves room for 30-40 interrupts
until we will get an
overflow. But we need in worst case space for 128 interrupts.
Is there a mistake in our analysis? Do other people have the same
problem and probably already
a solution? What options do we have?
Frank Haverkamp
& Joern Engel
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
Quoted 2 lines
What options do we have?
do_IRQ() keeps asking your get_irq() routine which irq to serice. Couldn't your get_irq() keep reporting pending requests until all (currently known) requests were satisfied? It isn't necessary to actually commence a nested instance of exception handling for every request, right?
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