[ovs-git] Open vSwitch: hmap_random_node: Improve distribution (master)

dev at openvswitch.org dev at openvswitch.org
Thu Apr 24 06:02:57 UTC 2014


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- Log -----------------------------------------------------------------
commit e58f91a15a38ad2d26d77b77b2f1c84f6c6b06dc
Diffs: http://openvswitch.org/cgi-bin/gitweb.cgi?p=openvswitch;a=commitdiff;h=e58f91a15a38ad2d26d77b77b2f1c84f6c6b06dc
Author: YAMAMOTO Takashi <yamamoto at valinux.co.jp>
		
hmap_random_node: Improve distribution
		
Improve random distribution for an hmap with a small number of nodes
with the expense of the increased cpu cost.
It would be a fair trade-off because the situation is rather common
for bond, which is currently the only consumer of this API in tree.

Consider 2 items, 4 buckets, no collision.

    bucket 0   item 0
    bucket 1
    bucket 2
    bucket 3   item 1

The old algorithm picks item 0 if rand % 4 == 0.  (25%)
Otherwise it picks item 1.  (75%)

This change makes them 50%.

Acked-by: Ben Pfaff <blp at nicira.com>
Signed-off-by: YAMAMOTO Takashi <yamamoto at valinux.co.jp>


-----------------------------------------------------------------------

Summary of changes:
 lib/hmap.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)


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