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Improve PRNG jumping when using threads

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Currently, when a new thread needs to use the RANDOM_NUMBER intrinsic,
the per-thread PRNG state is initialized by copying the master state
and then jumping forwards N*2**128 entries in the stream so that the
PRNG streams for different threads don't alias each other, where N is
the number of threads that have so far initialized the PRNG.

With this patch the master state itself is jumped forwards once each
time a new thread initializes the PRNG, thus obviating the need to
jump through all the N-1 previous streams. Effectively turning an O(N)
algorithm into an O(1) one.

Regtested on x86_64-pc-linux-gnu.

libgfortran/ChangeLog:

2019-09-05  Janne Blomqvist  <jb@gcc.gnu.org>

	* intrinsics/random.c (master_init): Replace with
	master_state.init.
	(njumps): Remove variable.
	(master_state): Make instance of struct prng_state.
	(init_rand_state): When jumping, update the master_state once
	instead of keeping track of how many jumps need to be done.
	(SZU64): Modify to handle new master_state.
	(SZ): Likewise.
	(random_seed_i4): Likewise.
	(random_seed_i8): Likewise.

From-SVN: r275397
This commit is contained in:
Janne Blomqvist 2019-09-05 09:59:55 +03:00
parent f44526e367
commit 0eaee4abb1
2 changed files with 32 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
libgfortran/ChangeLog
View File

@ -1,3 +1,16 @@
2019-09-05 Janne Blomqvist <jb@gcc.gnu.org>
* intrinsics/random.c (master_init): Replace with
master_state.init.
(njumps): Remove variable.
(master_state): Make instance of struct prng_state.
(init_rand_state): When jumping, update the master_state once
instead of keeping track of how many jumps need to be done.
(SZU64): Modify to handle new master_state.
(SZ): Likewise.
(random_seed_i4): Likewise.
(random_seed_i8): Likewise.
2019-08-17 Janne Blomqvist <jb@gcc.gnu.org>
PR fortran/68401

46
libgfortran/intrinsics/random.c
View File

@ -194,13 +194,10 @@ typedef struct
prng_state;
/* master_init, njumps, and master_state are the only variables
protected by random_lock. */
static bool master_init;
static unsigned njumps; /* How many times we have jumped. */
static uint64_t master_state[] = {
0xad63fa1ed3b55f36ULL, 0xd94473e78978b497ULL, 0xbc60592a98172477ULL,
0xa3de7c6e81265301ULL
/* master_state is the only variable protected by random_lock. */
static prng_state master_state = { .init = false, .s = {
0xad63fa1ed3b55f36ULL, 0xd94473e78978b497ULL, 0xbc60592a98172477ULL,
0xa3de7c6e81265301ULL }
};
@ -353,24 +350,21 @@ init_rand_state (prng_state* rs, const bool locked)
{
if (!locked)
__gthread_mutex_lock (&random_lock);
if (!master_init)
if (!master_state.init)
{
uint64_t os_seed;
getosrandom (&os_seed, sizeof (os_seed));
for (uint64_t i = 0; i < sizeof (master_state) / sizeof (uint64_t); i++)
for (uint64_t i = 0; i < sizeof (master_state.s) / sizeof (uint64_t); i++)
{
os_seed = splitmix64 (os_seed);
master_state[i] = os_seed;
master_state.s[i] = os_seed;
}
njumps = 0;
master_init = true;
master_state.init = true;
}
memcpy (&rs->s, master_state, sizeof (master_state));
unsigned n = njumps++;
memcpy (&rs->s, master_state.s, sizeof (master_state.s));
jump (&master_state);
if (!locked)
__gthread_mutex_unlock (&random_lock);
for (unsigned i = 0; i < n; i++)
jump (rs);
rs->init = true;
}
@ -727,7 +721,7 @@ arandom_r16 (gfc_array_r16 *x)
/* Number of elements in master_state array. */
#define SZU64 (sizeof (master_state) / sizeof (uint64_t))
#define SZU64 (sizeof (master_state.s) / sizeof (uint64_t))
/* Keys for scrambling the seed in order to avoid poor seeds. */
@ -757,7 +751,7 @@ void
random_seed_i4 (GFC_INTEGER_4 *size, gfc_array_i4 *put, gfc_array_i4 *get)
{
uint64_t seed[SZU64];
#define SZ (sizeof (master_state) / sizeof (GFC_INTEGER_4))
#define SZ (sizeof (master_state.s) / sizeof (GFC_INTEGER_4))
/* Check that we only have one argument present. */
if ((size ? 1 : 0) + (put ? 1 : 0) + (get ? 1 : 0) > 1)
@ -800,7 +794,7 @@ random_seed_i4 (GFC_INTEGER_4 *size, gfc_array_i4 *put, gfc_array_i4 *get)
a processor-dependent value to the seed." */
if (size == NULL && put == NULL && get == NULL)
{
master_init = false;
master_state.init = false;
init_rand_state (rs, true);
}
@ -822,9 +816,8 @@ random_seed_i4 (GFC_INTEGER_4 *size, gfc_array_i4 *put, gfc_array_i4 *get)
/* We put it after scrambling the bytes, to paper around users who
provide seeds with quality only in the lower or upper part. */
scramble_seed (master_state, seed);
njumps = 0;
master_init = true;
scramble_seed (master_state.s, seed);
master_state.init = true;
init_rand_state (rs, true);
}
@ -844,7 +837,7 @@ random_seed_i8 (GFC_INTEGER_8 *size, gfc_array_i8 *put, gfc_array_i8 *get)
if ((size ? 1 : 0) + (put ? 1 : 0) + (get ? 1 : 0) > 1)
runtime_error ("RANDOM_SEED should have at most one argument present.");
#define SZ (sizeof (master_state) / sizeof (GFC_INTEGER_8))
#define SZ (sizeof (master_state.s) / sizeof (GFC_INTEGER_8))
if (size != NULL)
*size = SZ;
@ -881,7 +874,7 @@ random_seed_i8 (GFC_INTEGER_8 *size, gfc_array_i8 *put, gfc_array_i8 *get)
a processor-dependent value to the seed." */
if (size == NULL && put == NULL && get == NULL)
{
master_init = false;
master_state.init = false;
init_rand_state (rs, true);
}
@ -900,9 +893,8 @@ random_seed_i8 (GFC_INTEGER_8 *size, gfc_array_i8 *put, gfc_array_i8 *get)
memcpy (&seed[i], &(put->base_addr[i * GFC_DESCRIPTOR_STRIDE(put,0)]),
sizeof (GFC_UINTEGER_8));
scramble_seed (master_state, seed);
njumps = 0;
master_init = true;
scramble_seed (master_state.s, seed);
master_state.init = true;
init_rand_state (rs, true);
}