Author: nbd Date: 2015-05-08 23:46:51 +0200 (Fri, 08 May 2015) New Revision: 45650
Added: trunk/target/linux/generic/patches-3.18/080-19-fib_trie-Use-index-0ul-n-bits-instead-of-index-n-bit.patch Log: kernel: add accidentally left out fib trie backport patch Signed-off-by: Felix Fietkau <[email protected]> Added: trunk/target/linux/generic/patches-3.18/080-19-fib_trie-Use-index-0ul-n-bits-instead-of-index-n-bit.patch =================================================================== --- trunk/target/linux/generic/patches-3.18/080-19-fib_trie-Use-index-0ul-n-bits-instead-of-index-n-bit.patch (rev 0) +++ trunk/target/linux/generic/patches-3.18/080-19-fib_trie-Use-index-0ul-n-bits-instead-of-index-n-bit.patch 2015-05-08 21:46:51 UTC (rev 45650) @@ -0,0 +1,52 @@ +From: Alexander Duyck <[email protected]> +Date: Thu, 22 Jan 2015 15:51:08 -0800 +Subject: [PATCH] fib_trie: Use index & (~0ul << n->bits) instead of index >> + n->bits + +In doing performance testing and analysis of the changes I recently found +that by shifting the index I had created an unnecessary dependency. + +I have updated the code so that we instead shift a mask by bits and then +just test against that as that should save us about 2 CPU cycles since we +can generate the mask while the key and pos are being processed. + +Signed-off-by: Alexander Duyck <[email protected]> +Signed-off-by: David S. Miller <[email protected]> +--- + +--- a/net/ipv4/fib_trie.c ++++ b/net/ipv4/fib_trie.c +@@ -961,12 +961,12 @@ static struct tnode *fib_find_node(struc + * prefix plus zeros for the bits in the cindex. The index + * is the difference between the key and this value. From + * this we can actually derive several pieces of data. +- * if !(index >> bits) +- * we know the value is cindex +- * else ++ * if (index & (~0ul << bits)) + * we have a mismatch in skip bits and failed ++ * else ++ * we know the value is cindex + */ +- if (index >> n->bits) ++ if (index & (~0ul << n->bits)) + return NULL; + + /* we have found a leaf. Prefixes have already been compared */ +@@ -1301,12 +1301,12 @@ int fib_table_lookup(struct fib_table *t + * prefix plus zeros for the "bits" in the prefix. The index + * is the difference between the key and this value. From + * this we can actually derive several pieces of data. +- * if !(index >> bits) +- * we know the value is child index +- * else ++ * if (index & (~0ul << bits)) + * we have a mismatch in skip bits and failed ++ * else ++ * we know the value is cindex + */ +- if (index >> n->bits) ++ if (index & (~0ul << n->bits)) + break; + + /* we have found a leaf. Prefixes have already been compared */ _______________________________________________ openwrt-commits mailing list [email protected] https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-commits
