netdev - Practical performance change to qdisc

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Message-ID: <1278085902.16508.149.camel@bwyatt>
Date:	Fri, 2 Jul 2010 10:51:42 -0500
From:	Bart <bwyatt@...lovmedia.com>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Practical performance change to qdisc_lookup

While looking to speed up our batch processing of many-thousands of TC
rules I stumbled across a usage-based optimization of qdisc_lookup().

while not a algorithmic optimization, I would wager that future rules
are likely to refer to the more recently created qdiscs and not the
oldest ones.

It is silly, but I thought I'd survey opinions on the change.  It is far
less code entropy than say, implementing a hash lookup.

sch_api.c:
@@ -197,7 +197,7 @@
 	    root->handle == handle)
 		return root;

-	list_for_each_entry(q, &root->list, list) {
+	list_for_each_entry_reverse(q, &root->list, list) {
 		if (q->handle == handle)
 			return q;
 	}

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