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Message-ID: <alpine.DEB.2.00.1011251520270.1198@blackhole.kfki.hu>
Date: Thu, 25 Nov 2010 15:41:08 +0100 (CET)
From: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
To: Eric Dumazet <eric.dumazet@...il.com>
cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org,
Linus Torvalds <torvalds@...l.org>,
Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 2/2] The new jhash implementation
On Thu, 25 Nov 2010, Eric Dumazet wrote:
> I agree jhash() should be not be inlined.
>
> I am not sure for other variants.
Yeah, I have got the same feelings. I decided to un-inline all of them
because that way the internal macros are not exposed at all.
> > +u32 jhash(const void *key, u32 length, u32 initval)
> > +{
> > + u32 a, b, c;
> > + const u8 *k = key;
> > +
> > + /* Set up the internal state */
> > + a = b = c = JHASH_INITVAL + length + initval;
> > +
> > + /* All but the last block: affect some 32 bits of (a,b,c) */
> > + while (length > 12) {
> > + a += k[0] + ((u32)k[1]<<8) + ((u32)k[2]<<16) + ((u32)k[3]<<24);
>
> disassembly code on x86_32 for the previous line :
>
> 26: 66 90 xchg %ax,%ax
> 28: 0f b6 72 01 movzbl 0x1(%edx),%esi
> 2c: 0f b6 4a 02 movzbl 0x2(%edx),%ecx
> 30: c1 e6 08 shl $0x8,%esi
> 33: c1 e1 10 shl $0x10,%ecx
> 36: 8d 0c 0e lea (%esi,%ecx,1),%ecx
> 39: 0f b6 32 movzbl (%edx),%esi
> 3c: 8d 34 31 lea (%ecx,%esi,1),%esi
> 3f: 0f b6 4a 03 movzbl 0x3(%edx),%ecx
> 43: c1 e1 18 shl $0x18,%ecx
> 46: 8d 0c 0e lea (%esi,%ecx,1),%ecx
>
> or (CONFIG_CC_OPTIMIZE_FOR_SIZE=y) :
>
> 1b: 0f b6 7b 01 movzbl 0x1(%ebx),%edi
> 1f: c1 e7 08 shl $0x8,%edi
> 22: 89 7d f0 mov %edi,-0x10(%ebp)
> 25: 0f b6 7b 02 movzbl 0x2(%ebx),%edi
> 29: c1 e7 10 shl $0x10,%edi
> 2c: 03 7d f0 add -0x10(%ebp),%edi
> 2f: 89 7d f0 mov %edi,-0x10(%ebp)
> 32: 0f b6 3b movzbl (%ebx),%edi
> 35: 03 7d f0 add -0x10(%ebp),%edi
> 38: 89 7d f0 mov %edi,-0x10(%ebp)
> 3b: 0f b6 7b 03 movzbl 0x3(%ebx),%edi
> 3f: c1 e7 18 shl $0x18,%edi
> 42: 03 7d f0 add -0x10(%ebp),%edi
>
>
> I suggest :
>
> #include <linux/unaligned/packed_struct.h>
> ...
> a += __get_unaligned_cpu32(k);
> b += __get_unaligned_cpu32(k+4);
> c += __get_unaligned_cpu32(k+8);
>
> Fits nicely in registers.
Good idea, thanks!
Here follows the updated second patch:
The current jhash.h implements the lookup2() hash function by Bob Jenkins.
However, lookup2() is outdated as Bob wrote a new hash function called
lookup3(). The new hash function
- mixes better than lookup2(): it passes the check that every input bit
changes every output bit 50% of the time, while lookup2() failed it.
- performs better: compiled with -O2 on Core2 Duo, lookup3() 20-40% faster
than lookup2() depending on the key length.
The patch replaces the lookup2() implementation of the 'jhash*'
functions with that of lookup3().
You can read a longer comparison of the two and other hash functions at
http://burtleburtle.net/bob/hash/doobs.html.
Signed-off-by: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
---
include/linux/jhash.h | 136 +++----------------------------------------
lib/Makefile | 2 +-
lib/jhash.c | 154 +++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 163 insertions(+), 129 deletions(-)
create mode 100644 lib/jhash.c
diff --git a/include/linux/jhash.h b/include/linux/jhash.h
index ced1159..ca69ac3 100644
--- a/include/linux/jhash.h
+++ b/include/linux/jhash.h
@@ -1,134 +1,14 @@
#ifndef _LINUX_JHASH_H
#define _LINUX_JHASH_H
-/* jhash.h: Jenkins hash support.
- *
- * Copyright (C) 1996 Bob Jenkins (bob_jenkins@...tleburtle.net)
- *
- * http://burtleburtle.net/bob/hash/
- *
- * These are the credits from Bob's sources:
- *
- * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
- * hash(), hash2(), hash3, and mix() are externally useful functions.
- * Routines to test the hash are included if SELF_TEST is defined.
- * You can use this free for any purpose. It has no warranty.
- *
- * Copyright (C) 2003 David S. Miller (davem@...hat.com)
- *
- * I've modified Bob's hash to be useful in the Linux kernel, and
- * any bugs present are surely my fault. -DaveM
- */
-
-/* NOTE: Arguments are modified. */
-#define __jhash_mix(a, b, c) \
-{ \
- a -= b; a -= c; a ^= (c>>13); \
- b -= c; b -= a; b ^= (a<<8); \
- c -= a; c -= b; c ^= (b>>13); \
- a -= b; a -= c; a ^= (c>>12); \
- b -= c; b -= a; b ^= (a<<16); \
- c -= a; c -= b; c ^= (b>>5); \
- a -= b; a -= c; a ^= (c>>3); \
- b -= c; b -= a; b ^= (a<<10); \
- c -= a; c -= b; c ^= (b>>15); \
-}
-
-/* The golden ration: an arbitrary value */
-#define JHASH_GOLDEN_RATIO 0x9e3779b9
-
-/* The most generic version, hashes an arbitrary sequence
- * of bytes. No alignment or length assumptions are made about
- * the input key.
- */
-static inline u32 jhash(const void *key, u32 length, u32 initval)
-{
- u32 a, b, c, len;
- const u8 *k = key;
-
- len = length;
- a = b = JHASH_GOLDEN_RATIO;
- c = initval;
-
- while (len >= 12) {
- a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
- b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
- c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
-
- __jhash_mix(a,b,c);
-
- k += 12;
- len -= 12;
- }
-
- c += length;
- switch (len) {
- case 11: c += ((u32)k[10]<<24);
- case 10: c += ((u32)k[9]<<16);
- case 9 : c += ((u32)k[8]<<8);
- case 8 : b += ((u32)k[7]<<24);
- case 7 : b += ((u32)k[6]<<16);
- case 6 : b += ((u32)k[5]<<8);
- case 5 : b += k[4];
- case 4 : a += ((u32)k[3]<<24);
- case 3 : a += ((u32)k[2]<<16);
- case 2 : a += ((u32)k[1]<<8);
- case 1 : a += k[0];
- };
-
- __jhash_mix(a,b,c);
-
- return c;
-}
-
-/* A special optimized version that handles 1 or more of u32s.
- * The length parameter here is the number of u32s in the key.
- */
-static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
-{
- u32 a, b, c, len;
-
- a = b = JHASH_GOLDEN_RATIO;
- c = initval;
- len = length;
-
- while (len >= 3) {
- a += k[0];
- b += k[1];
- c += k[2];
- __jhash_mix(a, b, c);
- k += 3; len -= 3;
- }
-
- c += length * 4;
-
- switch (len) {
- case 2 : b += k[1];
- case 1 : a += k[0];
- };
-
- __jhash_mix(a,b,c);
-
- return c;
-}
-
-
-/* A special ultra-optimized versions that knows they are hashing exactly
- * 3, 2 or 1 word(s).
- *
- * NOTE: In particular the "c += length; __jhash_mix(a,b,c);" normally
- * done at the end is not done here.
- */
-static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
-{
- a += JHASH_GOLDEN_RATIO;
- b += JHASH_GOLDEN_RATIO;
- c += initval;
-
- __jhash_mix(a, b, c);
-
- return c;
-}
+/* Best hash sizes are of power of two */
+#define jhash_size(n) ((u32)1<<(n))
+/* Mask the hash value, i.e (value & jhash_mask(n)) instead of (value % n) */
+#define jhash_mask(n) (jhash_size(n)-1)
+
+extern u32 jhash(const void *key, u32 length, u32 initval);
+extern u32 jhash2(const u32 *k, u32 length, u32 initval);
+extern u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval);
static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
{
diff --git a/lib/Makefile b/lib/Makefile
index e6a3763..a1a4932 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -10,7 +10,7 @@ endif
lib-y := ctype.o string.o vsprintf.o cmdline.o \
rbtree.o radix-tree.o dump_stack.o \
idr.o int_sqrt.o extable.o prio_tree.o \
- sha1.o irq_regs.o reciprocal_div.o argv_split.o \
+ jhash.o sha1.o irq_regs.o reciprocal_div.o argv_split.o \
proportions.o prio_heap.o ratelimit.o show_mem.o \
is_single_threaded.o plist.o decompress.o flex_array.o
diff --git a/lib/jhash.c b/lib/jhash.c
new file mode 100644
index 0000000..538277b
--- /dev/null
+++ b/lib/jhash.c
@@ -0,0 +1,154 @@
+/* jhash.c: Jenkins hash support.
+ *
+ * Copyright (C) 2006. Bob Jenkins (bob_jenkins@...tleburtle.net)
+ *
+ * http://burtleburtle.net/bob/hash/
+ *
+ * These are the credits from Bob's sources:
+ *
+ * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+ *
+ * These are functions for producing 32-bit hashes for hash table lookup.
+ * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
+ * are externally useful functions. Routines to test the hash are included
+ * if SELF_TEST is defined. You can use this free for any purpose. It's in
+ * the public domain. It has no warranty.
+ *
+ * Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@...ckhole.kfki.hu)
+ *
+ * I've modified Bob's hash to be useful in the Linux kernel, and
+ * any bugs present are my fault.
+ * Jozsef
+ */
+#include <linux/bitops.h>
+#include <linux/module.h>
+#include <linux/unaligned/packed_struct.h>
+#include <linux/jhash.h>
+
+/* __jhash_mix -- mix 3 32-bit values reversibly. */
+#define __jhash_mix(a, b, c) \
+{ \
+ a -= c; a ^= rol32(c, 4); c += b; \
+ b -= a; b ^= rol32(a, 6); a += c; \
+ c -= b; c ^= rol32(b, 8); b += a; \
+ a -= c; a ^= rol32(c, 16); c += b; \
+ b -= a; b ^= rol32(a, 19); a += c; \
+ c -= b; c ^= rol32(b, 4); b += a; \
+}
+
+/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
+#define __jhash_final(a, b, c) \
+{ \
+ c ^= b; c -= rol32(b, 14); \
+ a ^= c; a -= rol32(c, 11); \
+ b ^= a; b -= rol32(a, 25); \
+ c ^= b; c -= rol32(b, 16); \
+ a ^= c; a -= rol32(c, 4); \
+ b ^= a; b -= rol32(a, 14); \
+ c ^= b; c -= rol32(b, 24); \
+}
+
+/* An arbitrary initial parameter */
+#define JHASH_INITVAL 0xdeadbeef
+
+/* jhash - hash an arbitrary key
+ * @k: sequence of bytes as key
+ * @length: the length of the key
+ * @initval: the previous hash, or an arbitray value
+ *
+ * The generic version, hashes an arbitrary sequence of bytes.
+ * No alignment or length assumptions are made about the input key.
+ *
+ * Returns the hash value of the key. The result depends on endianness.
+ */
+u32 jhash(const void *key, u32 length, u32 initval)
+{
+ u32 a, b, c;
+ const u8 *k = key;
+
+ /* Set up the internal state */
+ a = b = c = JHASH_INITVAL + length + initval;
+
+ /* All but the last block: affect some 32 bits of (a,b,c) */
+ while (length > 12) {
+ a += __get_unaligned_cpu32(k);
+ b += __get_unaligned_cpu32(k + 4);
+ c += __get_unaligned_cpu32(k + 8);
+ __jhash_mix(a, b, c);
+ length -= 12;
+ k += 12;
+ }
+ /* Last block: affect all 32 bits of (c) */
+ /* All the case statements fall through */
+ switch (length) {
+ case 12: c += (u32)k[11]<<24;
+ case 11: c += (u32)k[10]<<16;
+ case 10: c += (u32)k[9]<<8;
+ case 9: c += k[8];
+ case 8: b += (u32)k[7]<<24;
+ case 7: b += (u32)k[6]<<16;
+ case 6: b += (u32)k[5]<<8;
+ case 5: b += k[4];
+ case 4: a += (u32)k[3]<<24;
+ case 3: a += (u32)k[2]<<16;
+ case 2: a += (u32)k[1]<<8;
+ case 1: a += k[0];
+ __jhash_final(a, b, c);
+ case 0: /* Nothing left to add */
+ break;
+ }
+
+ return c;
+}
+EXPORT_SYMBOL(jhash);
+
+/* jhash2 - hash an array of u32's
+ * @k: the key which must be an array of u32's
+ * @length: the number of u32's in the key
+ * @initval: the previous hash, or an arbitray value
+ *
+ * Returns the hash value of the key.
+ */
+u32 jhash2(const u32 *k, u32 length, u32 initval)
+{
+ u32 a, b, c;
+
+ /* Set up the internal state */
+ a = b = c = JHASH_INITVAL + (length<<2) + initval;
+
+ /* Handle most of the key */
+ while (length > 3) {
+ a += k[0];
+ b += k[1];
+ c += k[2];
+ __jhash_mix(a, b, c);
+ length -= 3;
+ k += 3;
+ }
+
+ /* Handle the last 3 u32's: all the case statements fall through */
+ switch (length) {
+ case 3: c += k[2];
+ case 2: b += k[1];
+ case 1: a += k[0];
+ __jhash_final(a, b, c);
+ case 0: /* Nothing left to add */
+ break;
+ }
+
+ return c;
+}
+EXPORT_SYMBOL(jhash2);
+
+/* jhash_3words - hash exactly 3, 2 or 1 word(s) */
+u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
+{
+ a += JHASH_INITVAL;
+ b += JHASH_INITVAL;
+ c += initval;
+
+ __jhash_mix(a, b, c);
+
+ return c;
+}
+EXPORT_SYMBOL(jhash_3words);
--
1.7.0.4
Best regards,
Jozsef
-
E-mail : kadlec@...ckhole.kfki.hu, kadlec@...l.kfki.hu
PGP key : http://www.kfki.hu/~kadlec/pgp_public_key.txt
Address : KFKI Research Institute for Particle and Nuclear Physics
H-1525 Budapest 114, POB. 49, Hungary
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