671047943d
Some RB tree users require quick access to the next and the previous node, e.g. to check whether a modification of the node results in a change of the nodes position in the tree. If the node position does not change, then the modification can happen in place without going through a full enqueue requeue cycle. A upcoming use case for this are the timer queues of the hrtimer subsystem as they can optimize for timers which are frequently rearmed while enqueued. This can be obviously achieved with rb_next() and rb_prev(), but those turned out to be quite expensive for hotpath operations depending on the tree depth. Add a linked RB tree variant where add() and erase() maintain the links between the nodes. Like the cached variant it provides a pointer to the left most node in the root. It intentionally does not use a [h]list head as there is no real need for true list operations as the list is strictly coupled to the tree and and cannot be manipulated independently. It sets the nodes previous pointer to NULL for the left most node and the next pointer to NULL for the right most node. This allows a quick check especially for the left most node without consulting the list head address, which creates better code. Aside of the rb_leftmost cached pointer this could trivially provide a rb_rightmost pointer as well, but there is no usage for that (yet). Signed-off-by: Thomas Gleixner <tglx@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/20260224163431.668401024@kernel.org |
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