Messages in this thread | | | Date | Sun, 28 Aug 2005 18:35:31 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] make radix tree gang lookup faster by using a bitmap search |
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James Bottomley <James.Bottomley@SteelEye.com> wrote: > > On Sun, 2005-08-28 at 17:52 -0700, Andrew Morton wrote: > > > +#if BITS_PER_LONG == 32 > > > +#define RADIX_TREE_MAP_SHIFT 5 > > > +#elif BITS_PER_LONG == 64 > > > ... > > > struct radix_tree_node { > > > - unsigned int count; > > > void *slots[RADIX_TREE_MAP_SIZE]; > > > - unsigned long tags[RADIX_TREE_TAGS][RADIX_TREE_TAG_LONGS]; > > > + unsigned long tags[RADIX_TREE_TAGS]; > > > }; > > > > I don't see why the above change was necessary? Why not stick with the > > current more flexible sizing option? > > > > Note that the RADIX_TREE_MAP_FULL trick can still be used. It just has to > > be put inside a `for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++)' loop, > > which will vanish if RADIX_TREE_TAG_LONGS==1. > > Well ... It's my opinion (and purely unsubstantiated, I suppose) that > it's more efficient on 32 bit platforms to do bit operations on 32 bit > quantities, which is why I changed the radix tree map shift to 5 for > that case. > > It also makes much cleaner code than having to open code checks on > variable sized bitmaps. >
It does make the tree higher and hence will incur some more cache missing when descending the tree.
We changed the node size a few years back. umm.... http://www.ussg.iu.edu/hypermail/linux/kernel/0206.2/0141.html
It would be a little bit sad to be unable to make such tuning adjustments in the future. Not a huge loss, but a loss. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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