* [PATCH] eal: have unregistered non-EAL threads use dedicated PRNG
@ 2022-12-05 10:03 Mattias Rönnblom
2022-12-05 10:58 ` Morten Brørup
2023-02-10 11:44 ` David Marchand
0 siblings, 2 replies; 4+ messages in thread
From: Mattias Rönnblom @ 2022-12-05 10:03 UTC (permalink / raw)
To: Thomas Monjalon, David Marchand; +Cc: dev, 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.ronnblom@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
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [PATCH] eal: have unregistered non-EAL threads use dedicated PRNG
2022-12-05 10:03 [PATCH] eal: have unregistered non-EAL threads use dedicated PRNG Mattias Rönnblom
@ 2022-12-05 10:58 ` Morten Brørup
2022-12-06 15:14 ` Mattias Rönnblom
2023-02-10 11:44 ` David Marchand
1 sibling, 1 reply; 4+ messages in thread
From: Morten Brørup @ 2022-12-05 10:58 UTC (permalink / raw)
To: Mattias Rönnblom, Thomas Monjalon, David Marchand; +Cc: dev
> From: Mattias Rönnblom [mailto:mattias.ronnblom@ericsson.com]
> Sent: Monday, 5 December 2022 11.04
>
> 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.ronnblom@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
>
A nice improvement.
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Here's some serious feature creep...
Instead of using "static struct rte_rand_state rand_states[RTE_MAX_LCORE + 1];", we could use thread local storage ("__tread rte_rand_state rand_state;") to keep the state per O/S thread (independent of lcore_id etc.), making it completely thread safe.
But then, how do we seed the state?
Currently, we use the RTE_INIT() constructor attribute to seed the array of rand_states; but there is no thread constructor attribute. So here comes the feature creep:
It would be very useful with RTE_THREAD_INIT()/_FINI constructor/destructor macros, so libraries and applications could define functions to be called by thread_func_wrapper() before/after calling tread_func.
Using arrays like some_variable[RTE_MAX_LCORE (+ 1)] is common practice in DPDK, but only really required for variables that are not private to the thread, i.e. variables that other threads need access to.
Per-thread constructors/destructors is a generic feature suggestion, so please don't hold back this rte_random patch!
-Morten
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] eal: have unregistered non-EAL threads use dedicated PRNG
2022-12-05 10:58 ` Morten Brørup
@ 2022-12-06 15:14 ` Mattias Rönnblom
0 siblings, 0 replies; 4+ messages in thread
From: Mattias Rönnblom @ 2022-12-06 15:14 UTC (permalink / raw)
To: Morten Brørup, Thomas Monjalon, David Marchand; +Cc: dev
On 2022-12-05 11:58, Morten Brørup wrote:
>> From: Mattias Rönnblom [mailto:mattias.ronnblom@ericsson.com]
>> Sent: Monday, 5 December 2022 11.04
>>
>> 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.ronnblom@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
>>
>
> A nice improvement.
>
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
>
>
Thanks Morten.
> Here's some serious feature creep...
>
> Instead of using "static struct rte_rand_state rand_states[RTE_MAX_LCORE + 1];", we could use thread local storage ("__tread rte_rand_state rand_state;") to keep the state per O/S thread (independent of lcore_id etc.), making it completely thread safe.
>
> But then, how do we seed the state?
>
> Currently, we use the RTE_INIT() constructor attribute to seed the array of rand_states; but there is no thread constructor attribute. So here comes the feature creep:
>
> It would be very useful with RTE_THREAD_INIT()/_FINI constructor/destructor macros, so libraries and applications could define functions to be called by thread_func_wrapper() before/after calling tread_func.
>
> Using arrays like some_variable[RTE_MAX_LCORE (+ 1)] is common practice in DPDK, but only really required for variables that are not private to the thread, i.e. variables that other threads need access to.
>
> Per-thread constructors/destructors is a generic feature suggestion, so please don't hold back this rte_random patch!
>
The performance (CPU & memory) implications of using TLS for the whole
per-thread data structure (a PRNG in this case), as opposed to the DPDK
pattern of keeping just an per-thread index in TLS and the rest in an
instance of a static array, is very unclear to me.
A middle ground would be to keep only a pointer in TLS, and have a lazy
allocation of an instance, when needed. I think you could solve the
seeding issue by having a lock-protected LCG for the purpose of seeding
(only).
For rte_random.c this is hair splitting, but considering this is a
general pattern, I think the discussion is relevant.
> -Morten
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] eal: have unregistered non-EAL threads use dedicated PRNG
2022-12-05 10:03 [PATCH] eal: have unregistered non-EAL threads use dedicated PRNG Mattias Rönnblom
2022-12-05 10:58 ` Morten Brørup
@ 2023-02-10 11:44 ` David Marchand
1 sibling, 0 replies; 4+ messages in thread
From: David Marchand @ 2023-02-10 11:44 UTC (permalink / raw)
To: Mattias Rönnblom; +Cc: Thomas Monjalon, dev
On Mon, Dec 5, 2022 at 11:08 AM Mattias Rönnblom
<mattias.ronnblom@ericsson.com> wrote:
>
> 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.ronnblom@ericsson.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Applied, thanks.
--
David Marchand
^ permalink raw reply [flat|nested] 4+ messages in thread
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