hash: cleanups

- Use __hash_u64() for __fill_random_buffer()
- Convert rdma to use GOLDEN_RATIO_64

That's the last user of GOLDEN_RATIO_PRIME, which due to bit sparseness
isn't really useful for our purposes.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/engines/rdma.c b/engines/rdma.c
index e3bb2567e0627b80cbe7183d5714bad23af7230e..fcb41068896de230ad4cd7f2b83064045eb0f122 100644 (file)
--- a/engines/rdma.c
+++ b/engines/rdma.c
@@ -1389,7 +1389,7 @@ static int fio_rdmaio_setup(struct thread_data *td)
                rd = malloc(sizeof(*rd));
 
                memset(rd, 0, sizeof(*rd));
-               init_rand_seed(&rd->rand_state, (unsigned int) GOLDEN_RATIO_PRIME, 0);
+               init_rand_seed(&rd->rand_state, (unsigned int) GOLDEN_RATIO_64, 0);
                td->io_ops_data = rd;
        }
 

diff --git a/hash.h b/hash.h
index f7596a56367572b2852d049144103979ead08eea..51f0706e2cc5cc5a310efaf43b86b3417ef8d198 100644 (file)
--- a/hash.h
+++ b/hash.h
@@ -9,32 +9,6 @@
    (C) 2002 William Lee Irwin III, IBM */
 
 /*
- * Knuth recommends primes in approximately golden ratio to the maximum
- * integer representable by a machine word for multiplicative hashing.
- * Chuck Lever verified the effectiveness of this technique:
- * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
- *
- * These primes are chosen to be bit-sparse, that is operations on
- * them can use shifts and additions instead of multiplications for
- * machines where multiplications are slow.
- */
-
-#if BITS_PER_LONG == 32
-/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
-#define GOLDEN_RATIO_PRIME 0x9e370001UL
-#elif BITS_PER_LONG == 64
-/*  2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
-#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
-#else
-#error Define GOLDEN_RATIO_PRIME for your wordsize.
-#endif
-
-/*
- * The above primes are actively bad for hashing, since they are
- * too sparse. The 32-bit one is mostly ok, the 64-bit one causes
- * real problems. Besides, the "prime" part is pointless for the
- * multiplicative hash.
- *
  * Although a random odd number will do, it turns out that the golden
  * ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
  * properties.

diff --git a/lib/rand.c b/lib/rand.c
index 1df1a7a049b9b14bb3c9334d4c2b7314e6168b07..1e669116f38ccac2c178ef7cbe850bd49ff02cc3 100644 (file)
--- a/lib/rand.c
+++ b/lib/rand.c
@@ -103,7 +103,7 @@ void __fill_random_buf(void *buf, unsigned int len, uint64_t seed)
 
        for (; b != e; ++b) {
                *b = seed;
-               seed *= GOLDEN_RATIO_64;
+               seed = __hash_u64(seed);
        }
 
        if (fio_unlikely(rest))