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author | peter <peter@FreeBSD.org> | 2001-03-17 05:43:01 +0000 |
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committer | peter <peter@FreeBSD.org> | 2001-03-17 05:43:01 +0000 |
commit | e0fe7f7124b88be1a6f4e1f21706133e107332a9 (patch) | |
tree | 411e80f251e3543837ace11efe5808bbccf32ced /sys/nfsclient/nfs_node.c | |
parent | 4b576c4ab58dae9b312f71e7d8878f92382c7d1d (diff) | |
download | FreeBSD-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/nfsclient/nfs_node.c')
-rw-r--r-- | sys/nfsclient/nfs_node.c | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/sys/nfsclient/nfs_node.c b/sys/nfsclient/nfs_node.c index 1ede795..365d7f2 100644 --- a/sys/nfsclient/nfs_node.c +++ b/sys/nfsclient/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); } /* |