[PATCH 2/2][RT] powerpc - Make the irq reverse mapping radix tree lockless

[Nick Piggin]

On Thursday 24 July 2008 20:50, Sebastien Dugue wrote:
> From: Sebastien Dugue <sebastien.dugue at bull.net>
> Date: Tue, 22 Jul 2008 11:56:41 +0200
> Subject: [PATCH][RT] powerpc - Make the irq reverse mapping radix tree
> lockless
>
>   The radix tree used by interrupt controllers for their irq reverse
> mapping (currently only the XICS found on pSeries) have a complex locking
> scheme dating back to before the advent of the concurrent radix tree on
> preempt-rt.
>
>   Take advantage of this and of the fact that the items of the tree are
> pointers to a static array (irq_map) elements which can never go under us
> to simplify the locking.
>
>   Concurrency between readers and writers are handled by the intrinsic
> properties of the concurrent radix tree. Concurrency between the tree
> initialization which is done asynchronously with readers and writers access
> is handled via an atomic variable (revmap_trees_allocated) set when the
> tree has been initialized and checked before any reader or writer access
> just like we used to check for tree.gfp_mask != 0 before.

Hmm, RCU radix tree is in mainline too for quite a while. I thought
Ben had already converted this code over ages ago...

Nothing against the -rt patch, but mainline should probably be updated
to use RCU as well?