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authorpeter <peter@FreeBSD.org>2001-03-17 05:43:01 +0000
committerpeter <peter@FreeBSD.org>2001-03-17 05:43:01 +0000
commite0fe7f7124b88be1a6f4e1f21706133e107332a9 (patch)
tree411e80f251e3543837ace11efe5808bbccf32ced /sys/nfs
parent4b576c4ab58dae9b312f71e7d8878f92382c7d1d (diff)
downloadFreeBSD-src-e0fe7f7124b88be1a6f4e1f21706133e107332a9.zip
FreeBSD-src-e0fe7f7124b88be1a6f4e1f21706133e107332a9.tar.gz
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
Diffstat (limited to 'sys/nfs')
-rw-r--r--sys/nfs/nfs_node.c24
1 files changed, 16 insertions, 8 deletions
diff --git a/sys/nfs/nfs_node.c b/sys/nfs/nfs_node.c
index 1ede795..365d7f2 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);
}
/*
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