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0e39ed0004
Currently, all fib hash tables use the same hashing function. This leads to a situation where feeding routes through a pipe from one table to another causes significant number of collisions, as routes are fed in the order of increasing hash values, but dst tables are sized based on the number of stored routes. The patch makes fib hashing function parametric and chooses random parameter for each table. Also generally improves quality of hashing functions. Unfortunately, while this patch fixes the issue with initial collisions, having different hashing functions leads to 2x slowdown of pipe feeding, presumably due to worse cache behavior in dst tables. Also, the original issue significantly affects just the initial part of feed, when the dst table is small, so even ideal fix would not improve that much. Therefore, no merge for this patch.
49 lines
1.2 KiB
C
49 lines
1.2 KiB
C
/*
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* BIRD Library -- Generic Bit Operations
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*
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* (c) 1998 Martin Mares <mj@ucw.cz>
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*
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* Can be freely distributed and used under the terms of the GNU GPL.
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*/
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#ifndef _BIRD_BITOPTS_H_
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#define _BIRD_BITOPTS_H_
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#include "sysdep/config.h"
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/*
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* Bit mask operations:
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*
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* u32_mkmask Make bit mask consisting of <n> consecutive ones
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* from the left and the rest filled with zeroes.
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* E.g., u32_mkmask(5) = 0xf8000000.
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* u32_masklen Inverse operation to u32_mkmask, -1 if not a bitmask.
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*/
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u32 u32_mkmask(uint n);
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uint u32_masklen(u32 x);
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u32 u32_log2(u32 v);
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static inline u64 u32_hash0(u32 v, u32 p, u64 acc)
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{ return (acc + v) * p; }
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static inline u32 u32_hash(u32 v)
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{ return hash_value(u32_hash0(v, HASH_PARAM, 0)); }
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static inline u64 u64_hash0(u64 v, u32 p, u64 acc)
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{ return u32_hash0(v >> 32, p, u32_hash0(v, p, acc)); }
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static inline u32 u64_hash(u64 v)
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{ return hash_value(u64_hash0(v, HASH_PARAM, 0)); }
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static inline u8 u32_popcount(u32 v) { return __builtin_popcount(v); }
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static inline u8 u64_popcount(u64 v) { return __builtin_popcountll(v); }
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static inline int u32_clz(u32 v) { return __builtin_clz(v); }
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static inline int u32_ctz(u32 v) { return __builtin_ctz(v); }
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static inline int uint_is_pow2(uint n) { return n && !(n & (n-1)); }
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#endif
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