mirror of
https://github.com/openvswitch/ovs
synced 2025-10-25 15:07:05 +00:00
c49d1dd168
murmurhash is faster than Jenkins and slightly higher quality, so switch to it for hashing words. The best timings I got for hashing for data lengths of the following numbers of 32-bit words, in seconds per 1,000,000,000 hashes, were: words murmurhash Jenkins hash ----- ---------- ------------ 1 8.4 10.4 2 10.3 10.3 3 11.2 10.7 4 12.6 18.0 5 13.9 18.3 6 15.2 18.7 In other words, murmurhash outperforms Jenkins for all input lengths other than exactly 3 32-bit words (12 bytes). (It's understandable that Jenkins would have a best case at 12 bytes, because Jenkins works in 12-byte chunks.) Even in the case where Jenkins is faster, it's only by 5%. On average within this data set, murmurhash is 15% faster, and for 4-word input it is 30% faster. We retain Jenkins for flow_hash_symmetric_l4() and flow_hash_fields(), which are cases where the hash value is exposed externally. This commit appears to improve "ovs-benchmark rate" results slightly by a few hundred connections per second (under 1%), when used with an NVP controller. Signed-off-by: Ben Pfaff <blp@nicira.com> Acked-by: Ethan Jackson <ethan@nicira.com>
77 lines
1.9 KiB
C
77 lines
1.9 KiB
C
/*
|
|
* Copyright (c) 2008, 2009, 2010, 2012, 2013 Nicira, Inc.
|
|
*
|
|
* Licensed under the Apache License, Version 2.0 (the "License");
|
|
* you may not use this file except in compliance with the License.
|
|
* You may obtain a copy of the License at:
|
|
*
|
|
* http://www.apache.org/licenses/LICENSE-2.0
|
|
*
|
|
* Unless required by applicable law or agreed to in writing, software
|
|
* distributed under the License is distributed on an "AS IS" BASIS,
|
|
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
* See the License for the specific language governing permissions and
|
|
* limitations under the License.
|
|
*/
|
|
#include <config.h>
|
|
#include "hash.h"
|
|
#include <string.h>
|
|
#include "unaligned.h"
|
|
|
|
/* Returns the hash of 'a', 'b', and 'c'. */
|
|
uint32_t
|
|
hash_3words(uint32_t a, uint32_t b, uint32_t c)
|
|
{
|
|
return mhash_finish(mhash_add(mhash_add(mhash_add(a, 0), b), c), 12);
|
|
}
|
|
|
|
/* Returns the hash of the 'n' bytes at 'p', starting from 'basis'. */
|
|
uint32_t
|
|
hash_bytes(const void *p_, size_t n, uint32_t basis)
|
|
{
|
|
const uint8_t *p = p_;
|
|
size_t orig_n = n;
|
|
uint32_t hash;
|
|
|
|
hash = basis;
|
|
while (n >= 4) {
|
|
hash = mhash_add(hash, get_unaligned_u32((const uint32_t *) p));
|
|
n -= 4;
|
|
p += 4;
|
|
}
|
|
|
|
if (n) {
|
|
uint32_t tmp = 0;
|
|
|
|
memcpy(&tmp, p, n);
|
|
hash = mhash_add__(hash, tmp);
|
|
}
|
|
|
|
return mhash_finish(hash, orig_n);
|
|
}
|
|
|
|
/* Returns the hash of the 'n' 32-bit words at 'p', starting from 'basis'.
|
|
* 'p' must be properly aligned. */
|
|
uint32_t
|
|
hash_words(const uint32_t p[], size_t n_words, uint32_t basis)
|
|
{
|
|
uint32_t hash;
|
|
size_t i;
|
|
|
|
hash = basis;
|
|
for (i = 0; i < n_words; i++) {
|
|
hash = mhash_add(hash, p[i]);
|
|
}
|
|
return mhash_finish(hash, n_words * 4);
|
|
}
|
|
|
|
uint32_t
|
|
hash_double(double x, uint32_t basis)
|
|
{
|
|
uint32_t value[2];
|
|
BUILD_ASSERT_DECL(sizeof x == sizeof value);
|
|
|
|
memcpy(value, &x, sizeof value);
|
|
return hash_3words(value[0], value[1], basis);
|
|
}
|