From e5a2c899957659cd1a9f789bc462f9c0b35f5150 Mon Sep 17 00:00:00 2001 From: Hannes Frederic Sowa Date: Wed, 5 Nov 2014 00:23:04 +0100 Subject: fast_hash: avoid indirect function calls By default the arch_fast_hash hashing function pointers are initialized to jhash(2). If during boot-up a CPU with SSE4.2 is detected they get updated to the CRC32 ones. This dispatching scheme incurs a function pointer lookup and indirect call for every hashing operation. rhashtable as a user of arch_fast_hash e.g. stores pointers to hashing functions in its structure, too, causing two indirect branches per hashing operation. Using alternative_call we can get away with one of those indirect branches. Acked-by: Daniel Borkmann Cc: Thomas Graf Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- include/linux/hash.h | 34 ---------------------------------- 1 file changed, 34 deletions(-) (limited to 'include/linux/hash.h') diff --git a/include/linux/hash.h b/include/linux/hash.h index d0494c399392..6e8fb028848c 100644 --- a/include/linux/hash.h +++ b/include/linux/hash.h @@ -84,38 +84,4 @@ static inline u32 hash32_ptr(const void *ptr) return (u32)val; } -struct fast_hash_ops { - u32 (*hash)(const void *data, u32 len, u32 seed); - u32 (*hash2)(const u32 *data, u32 len, u32 seed); -}; - -/** - * arch_fast_hash - Caclulates a hash over a given buffer that can have - * arbitrary size. This function will eventually use an - * architecture-optimized hashing implementation if - * available, and trades off distribution for speed. - * - * @data: buffer to hash - * @len: length of buffer in bytes - * @seed: start seed - * - * Returns 32bit hash. - */ -extern u32 arch_fast_hash(const void *data, u32 len, u32 seed); - -/** - * arch_fast_hash2 - Caclulates a hash over a given buffer that has a - * size that is of a multiple of 32bit words. This - * function will eventually use an architecture- - * optimized hashing implementation if available, - * and trades off distribution for speed. - * - * @data: buffer to hash (must be 32bit padded) - * @len: number of 32bit words - * @seed: start seed - * - * Returns 32bit hash. - */ -extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed); - #endif /* _LINUX_HASH_H */ -- cgit v1.2.3-59-g8ed1b