Dramatically improve the **lame** nfs_hash(). This is based on the

Fowler / Noll / Vo Hash (http://www.isthe.com/chongo/tech/comp/fnv/).

This improves hash coverage a *massive* amount.  We were seeing one
set of machines that were using 0.84% of their 131072 entry nfsnode
hash buckets with maximum chain lengths of up to ~500 entries.  The
machine was spending nearly 100% of its time in 'system'.
A test with this has pushed the coverage from a few perCent up to 91%
utilization with a max chain length of 11.

Submitted by:  David Filo

1 files changed, 16 insertions, 8 deletions

diff --git a/sys/nfs/nfs_node.c b/sys/nfs/nfs_node.c
index 1ede795ffdb5..365d7f2c20dd 100644
--- a/sys/nfs/nfs_node.c
+++ b/sys/nfs/nfs_node.c
@@ -73,21 +73,29 @@ nfs_nhinit()
 
 /*
  * Compute an entry in the NFS hash table structure
+ *
+ * Hash based on: http://www.isthe.com/chongo/tech/comp/fnv/
+ * by Glenn Fowler, Phong Vo and Landon Curt Noll
+ * aka the "Fowler / Noll / Vo Hash" (FNV)
  */
+#define FNV_32_PRIME ((u_int32_t) 0x01000193UL)
+#define FNV1_32_INIT ((u_int32_t) 33554467UL)
 u_long
 nfs_hash(fhp, fhsize)
-	register nfsfh_t *fhp;
+	nfsfh_t *fhp;
 	int fhsize;
 {
-	register u_char *fhpp;
-	register u_long fhsum;
-	register int i;
+	u_char *fhpp;
+	u_int32_t hval;
+	int i;
 
 	fhpp = &fhp->fh_bytes[0];
-	fhsum = 0;
-	for (i = 0; i < fhsize; i++)
-		fhsum += *fhpp++;
-	return (fhsum);
+	hval = FNV1_32_INIT;
+	for (i = 0; i < fhsize; i++) {
+		hval *= FNV_32_PRIME;
+		hval ^= (u_int32_t)*fhpp++;
+	}
+	return (hval);
 }
 
 /*