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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>
45 lines
1.3 KiB
C
45 lines
1.3 KiB
C
/*
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* Copyright (c) 2008, 2009, 2010, 2012 Nicira, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef JHASH_H
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#define JHASH_H 1
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#include <stdbool.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <string.h>
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#include "util.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* This is the public domain lookup3 hash by Bob Jenkins from
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* http://burtleburtle.net/bob/c/lookup3.c, modified for style.
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*
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* Use the functions in hash.h instead if you can. These are here just for
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* places where we've exposed a hash function "on the wire" and don't want it
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* to change. */
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uint32_t jhash_words(const uint32_t *, size_t n_word, uint32_t basis);
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uint32_t jhash_bytes(const void *, size_t n_bytes, uint32_t basis);
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#ifdef __cplusplus
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}
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#endif
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#endif /* jhash.h */
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