David Miller wrote:
From: Daniel Hellstrom <daniel@xxxxxxxxxxx>
Date: Thu, 16 Dec 2010 15:24:02 +0100
Why is IRQ15, the non-maskable IRQ, used for cross calls? Would it not
be safer to use IRQ14?
Since IRQ15 is non-maskable it will even interrupt spin_lock_irqsave()
protected reqions. I assume it is safe as long as the cross call
function run in IRQ context does not try to take the same spinlock,
for that would create a dead lock I believe. For example atomic_add()
on SPARC32 below is implemented using one of four global spinlocks,
does that mean that we can not use atomic functions at all from within
a cross call function?
We don't want operations like TLB and cache flushes to be blocked
by IRQ disabling.
For other operations, we should reschedule it to a software interrupt
at a lower level than 15, but nobody has done the work to implement
this yet.
Thank you for your answer.
I will try to create a patch for the atomic layer for SMP LEON systems
since they have the CASA instruction.
Thanks,
Daniel
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