Re: [PATCH] dentry and inode cache hash algorithm performance changes.

["Jose R. Santos" <jrsantos@austin.ibm.com>]

On 04/30/04 15:57:01, Jose R. Santos wrote:
> err... Wrote the patch to fast.  It should read
> 
> 	tmp = (hashval * sb) ^ (GOLDEN_RATIO_PRIME + hashval) / L1_CACHE_BYTES
> 
> I screw up... I'll send a fixed patch in a while.

Just notice I've made another error in the inode hash code.

Fixed patch (I hope) with beautification.

-JRS


diff -Nru a/fs/dcache.c b/fs/dcache.c
--- a/fs/dcache.c	Fri Apr 30 16:27:41 2004
+++ b/fs/dcache.c	Fri Apr 30 16:27:41 2004
@@ -28,6 +28,7 @@
 #include <asm/uaccess.h>
 #include <linux/security.h>
 #include <linux/seqlock.h>
+#include <linux/hash.h>
 
 #define DCACHE_PARANOIA 1
 /* #define DCACHE_DEBUG 1 */
@@ -799,8 +800,8 @@
 
 static inline struct hlist_head * d_hash(struct dentry * parent, unsigned long hash)
 {
-	hash += (unsigned long) parent / L1_CACHE_BYTES;
-	hash = hash ^ (hash >> D_HASHBITS);
+	hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
+	hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
 	return dentry_hashtable + (hash & D_HASHMASK);
 }
 
diff -Nru a/fs/inode.c b/fs/inode.c
--- a/fs/inode.c	Fri Apr 30 16:27:41 2004
+++ b/fs/inode.c	Fri Apr 30 16:27:41 2004
@@ -671,12 +671,13 @@
 
 static inline unsigned long hash(struct super_block *sb, unsigned long hashval)
 {
-	unsigned long tmp = hashval + ((unsigned long) sb / L1_CACHE_BYTES);
-	tmp = tmp + (tmp >> I_HASHBITS);
+	unsigned long tmp;
+	
+	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
+			L1_CACHE_BYTES;
+	tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
 	return tmp & I_HASHMASK;
 }
-
-/* Yeah, I know about quadratic hash. Maybe, later. */
 
 /**
  *	iunique - get a unique inode number