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 <dborkman@redhat.com>
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 0 insertions, 34 deletions

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 */