Re: [dpdk-dev] [PATCH 3/6] eal: improve entropy for initial PRNG seed

[Bruce Richardson <bruce.richardson@intel.com>]

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On Tue, May 14, 2019 at 11:20:43AM +0200, Mattias Rönnblom wrote:
> Replace the use of rte_get_timer_cycles() with getentropy() for
> seeding the pseudo-random number generator. getentropy() provides a
> more truly random value.
> 
> Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> ---
>  lib/librte_eal/common/rte_random.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_eal/common/rte_random.c b/lib/librte_eal/common/rte_random.c
> index 4d3cf5226..aafc2f7ad 100644
> --- a/lib/librte_eal/common/rte_random.c
> +++ b/lib/librte_eal/common/rte_random.c
> @@ -3,6 +3,7 @@
>   */
>  
>  #include <stdlib.h>
> +#include <unistd.h>
>  
>  #include <rte_branch_prediction.h>
>  #include <rte_cycles.h>
> @@ -135,5 +136,14 @@ rte_rand(void)
>  
>  RTE_INIT(rte_rand_init)
>  {
> -	rte_srand(rte_get_timer_cycles());
> +	uint64_t seed;
> +	int rc;
> +
> +	rc = getentropy(&seed, sizeof(seed));

This API was only introduced in FreeBSD in v12, so you may want to have a
define for enabling it, and (for meson) but in a check for
cc.has_function(get_entropy).

> +
> +	/* fall back to rdtsc in case of failure */
> +	if (rc < 0)
> +		seed = rte_get_timer_cycles();

Rather than fallback immediately to time, what about putting in a call to
HW random number generator support if available, e.g. rdseed instruction.

> +
> +	rte_srand(seed);
>  }
> -- 
> 2.17.1
>