netdev - [net PATCH] fib_trie: Drop unnecessary calls to leaf_pull

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Message-ID: <20150727195631.26840.93266.stgit@ahduyck-vm-fedora22>
Date:	Mon, 27 Jul 2015 13:08:06 -0700
From:	Alexander Duyck <alexander.h.duyck@...hat.com>
To:	dsa@...ulusnetworks.com, davem@...emloft.net
Cc:	netdev@...r.kernel.org
Subject: [net PATCH] fib_trie: Drop unnecessary calls to leaf_pull_suffix

It was reported that update_suffix was taking a long time on systems where
a large number of leaves were attached to a single node.  As it turns out
fib_table_flush was calling update_suffix for each leaf that didn't have all
of the aliases stripped from it.  As a result, on this large node removing
one leaf would result in us calling update_suffix for every other leaf on
the node.

The fix is to just remove the calls to leaf_pull_suffix since they are
redundant as we already have a call in resize that will go through and
update the suffix length for the node before we exit out of
fib_table_flush or fib_table_flush_external.

Reported-by: David Ahern <dsa@...ulusnetworks.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@...hat.com>
---

This patch should apply to linux-4.1.y and newer kernels.

I've done a bit of testing on my system and I no longer see update_suffix
dominating the performance traces.  David if you can test with this patch
to see if you still see the issue I would appreciate it.

 net/ipv4/fib_trie.c |    4 ----
 1 file changed, 4 deletions(-)

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index ef90d73911de..70168ca4716b 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1791,8 +1791,6 @@ void fib_table_flush_external(struct fib_table *tb)
 		if (hlist_empty(&n->leaf)) {
 			put_child_root(pn, n->key, NULL);
 			node_free(n);
-		} else {
-			leaf_pull_suffix(pn, n);
 		}
 	}
 }
@@ -1862,8 +1860,6 @@ int fib_table_flush(struct fib_table *tb)
 		if (hlist_empty(&n->leaf)) {
 			put_child_root(pn, n->key, NULL);
 			node_free(n);
-		} else {
-			leaf_pull_suffix(pn, n);
 		}
 	}

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