[PATCH] eal: have unregistered non-EAL threads use dedicated PRNG

[Mattias Rönnblom]

Prior to this change, unregistered non-EAL threads shared a PRNG
instance with the main lcore. The main lcore may well be used for fast
path processing, potentially making rte_rand() calls in the
process. It should not need to synchronize with control threads.

With this change, all unregistered non-EAL threads share one dedicated
PRNG instance.

The API documentation is updated to use the proper terminology when
referring to threads equipped with an lcore id.

Signed-off-by: Mattias Rönnblom <mattias.ronnb...@ericsson.com>
---
 lib/eal/common/rte_random.c  | 17 +++++++++++------
 lib/eal/include/rte_random.h | 10 +++++++---
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/lib/eal/common/rte_random.c b/lib/eal/common/rte_random.c
index 166b0d8921..565f2401ce 100644
--- a/lib/eal/common/rte_random.c
+++ b/lib/eal/common/rte_random.c
@@ -20,7 +20,11 @@ struct rte_rand_state {
        uint64_t z5;
 } __rte_cache_aligned;
 
-static struct rte_rand_state rand_states[RTE_MAX_LCORE];
+/* One instance each for every lcore id-equipped thread, and one
+ * additional instance to be shared by all others threads (i.e., all
+ * unregistered non-EAL threads).
+ */
+static struct rte_rand_state rand_states[RTE_MAX_LCORE + 1];
 
 static uint32_t
 __rte_rand_lcg32(uint32_t *seed)
@@ -114,14 +118,15 @@ __rte_rand_lfsr258(struct rte_rand_state *state)
 static __rte_always_inline
 struct rte_rand_state *__rte_rand_get_state(void)
 {
-       unsigned int lcore_id;
+       unsigned int idx;
 
-       lcore_id = rte_lcore_id();
+       idx = rte_lcore_id();
 
-       if (unlikely(lcore_id == LCORE_ID_ANY))
-               lcore_id = rte_get_main_lcore();
+       /* last instance reserved for unregistered non-EAL threads */
+       if (unlikely(idx == LCORE_ID_ANY))
+               idx = RTE_MAX_LCORE;
 
-       return &rand_states[lcore_id];
+       return &rand_states[idx];
 }
 
 uint64_t
diff --git a/lib/eal/include/rte_random.h b/lib/eal/include/rte_random.h
index d90e4d2192..2edf5d210b 100644
--- a/lib/eal/include/rte_random.h
+++ b/lib/eal/include/rte_random.h
@@ -41,7 +41,8 @@ rte_srand(uint64_t seedval);
  *
  * The generator is not cryptographically secure.
  *
- * If called from lcore threads, this function is thread-safe.
+ * If called from EAL threads or registered non-EAL threads, this function
+ * is thread-safe.
  *
  * @return
  *   A pseudo-random value between 0 and (1<<64)-1.
@@ -55,7 +56,8 @@ rte_rand(void);
  * This function returns an uniformly distributed (unbiased) random
  * number less than a user-specified maximum value.
  *
- * If called from lcore threads, this function is thread-safe.
+ * If called from EAL threads or registered non-EAL threads, this function
+ * is thread-safe.
  *
  * @param upper_bound
  *   The upper bound of the generated number.
@@ -75,7 +77,9 @@ rte_rand_max(uint64_t upper_bound);
  * number uniformly distributed over the interval [0.0, 1.0).
  *
  * The generator is not cryptographically secure.
- * If called from lcore threads, this function is thread-safe.
+ *
+ * If called from EAL threads or registered non-EAL threads, this function
+ * is thread-safe.
  *
  * @return
  *   A pseudo-random value between 0 and 1.0.
-- 
2.34.1