iptables/libiptc perf issue: Sorting chain during pull-out

Performance optimize scalability issue:
  Sorting chain during pull-out give worst-case runtime O(Chains2).

When pulling out the blob, every chain name is inserted alphabetically
into a linked list (by function iptc_insert_chain()).  The problem
with this approach is that the chain names delivered in the blob is
already sorted (as we push it back to the kernel sorted).

This cause chain parsing to always process every element in the chain
list and finish with a tail add.  Causing worst-case runtime O(C2/2)
for alphabetically sorting of chains.

The patch solves this by only calling iptc_insert_chain() when
creating new chains.

Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>

diff --git a/libiptc/libiptc.c b/libiptc/libiptc.c
index 472b81e01928b529ddbb890896f660ec024eb74e..e7ffb01b4b1e2dc283348eb7277f76d9bf026d5f 100644 (file)
--- a/libiptc/libiptc.c
+++ b/libiptc/libiptc.c
@@ -420,8 +420,8 @@ static void __iptcc_p_add_chain(TC_HANDLE_T h, struct chain_head *c,
        c->head_offset = offset;
        c->index = *num;
 
-       iptc_insert_chain(h, c);
-       
+       list_add_tail(&c->list, &h->chains); /* Its already sorted */
+
        h->chain_iterator_cur = c;
 }
 
@@ -1791,7 +1791,7 @@ TC_CREATE_CHAIN(const IPT_CHAINLABEL chain, TC_HANDLE_T *handle)
        }
 
        DEBUGP("Creating chain `%s'\n", chain);
-       list_add_tail(&c->list, &(*handle)->chains);
+       iptc_insert_chain(*handle, c); /* Insert sorted */
 
        set_changed(*handle);