The current sparse_irq allocator has several short comings due to
failures in the design or the lack of it:
- Requires iteration over the number of active irqs to find a free slot
(Some architectures have grown their own workarounds for this)
- Removal of entries is not possible
- Racy between create_irq_nr and destroy_irq (plugged by horrible
callbacks)
- Migration of active irq descriptors is not possible
- No bulk allocation of irq ranges
- Sprinkeled irq_desc references all over the place outside of kernel/irq/
(The previous chip functions series is addressing this issue)
Implement a sane allocator which fixes the above short comings (though
migration of active descriptors needs a full tree wide cleanup of the
direct and mostly unlocked access to irq_desc).
The new allocator still uses a radix_tree, but uses a bitmap for
keeping track of allocated irq numbers. That allows:
- Fast lookup of a free slot
- Allows the removal of descriptors
- Prevents the create/destroy race
- Bulk allocation of consecutive irq ranges
- Basic design is ready for migration of life descriptors after
further cleanups
The bitmap is also used in the SPARSE_IRQ=n case for lookup and
raceless (de)allocation of irq numbers. So it removes the requirement
for looping through the descriptor array to find slots.
Right now it uses sparse_irq_lock to protect the bitmap and the radix
tree, but after cleaning up all users we should be able convert that
to a mutex and to switch the radix_tree and decriptor allocations to
GFP_KERNEL.
[ Folded in a bugfix from Yinghai Lu ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
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