Messages in this thread | | | Date | Fri, 1 Nov 2002 20:55:32 +0000 | From | Jamie Lokier <> | Subject | Re: rbtree scores (was Re: [patch] deadline-ioscheduler rb-tree sort) |
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Andrew Morton wrote: > Jens Axboe wrote: > > > > As expected, the stock version O(N) insertion scan really hurts. Even > > with 128 requests per list, rbtree version is far superior. Once bigger > > lists are used, there's just no comparison whatsoever. > > > > Jens, the tree just makes sense.
Just a few comments about data structures - not important.
Technically I think that a priority queue, i.e. a heap (partially ordered tree) is sufficient for the request queue. I don't know the request queue code well enough to be sure, though.
Both heaps and trees are O(N log N), the difference being that an rbtree does a bit more constant-time work to balance the tree while maintaining a stricter ordering.
If it was worth it (I suspect not), you can make a data structure which has O(1) amortised insertion time for a number of common cases, such as runs of ascending block numbers. Seems a likely pattern for a filesystem...
Implementing the latter would likely be a lot of work for little gain though.
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