Re: [PATCH v5] enhance NUMA affinity heuristic

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 2/1/2023 12:20 PM, Kaisen You wrote:
> Trying to allocate memory on the first detected numa node has less
> chance to find some memory actually available rather than on the main
> lcore numa node (especially when the DPDK application is started only
> on one numa node).
> 
> Fixes: 705356f0811f ("eal: simplify control thread creation")
> Fixes: bb0bd346d5c1 ("eal: suggest using --lcores option")
> Cc: stable@dpdk.org
> 
> Signed-off-by: David Marchand <david.marchand@redhat.com>
> Signed-off-by: Kaisen You <kaisenx.you@intel.com>
> ---
> Changes since v4:
> - mod the patch title,
> 
> Changes since v3:
> - add the assignment of socket_id in thread initialization,
> 
> Changes since v2:
> - add uncommitted local change and fix compilation,
> 
> Changes since v1:
> - accomodate for configurations with main lcore running on multiples
>    physical cores belonging to different numa,
> ---
>   lib/eal/common/eal_common_thread.c | 1 +
>   lib/eal/common/malloc_heap.c       | 4 ++++
>   2 files changed, 5 insertions(+)
> 
> diff --git a/lib/eal/common/eal_common_thread.c b/lib/eal/common/eal_common_thread.c
> index 38d83a6885..21bff971f8 100644
> --- a/lib/eal/common/eal_common_thread.c
> +++ b/lib/eal/common/eal_common_thread.c
> @@ -251,6 +251,7 @@ static void *ctrl_thread_init(void *arg)
>   	void *routine_arg = params->arg;
>   
>   	__rte_thread_init(rte_lcore_id(), cpuset);
> +	RTE_PER_LCORE(_socket_id) = SOCKET_ID_ANY;
>   	params->ret = rte_thread_set_affinity_by_id(rte_thread_self(), cpuset);
>   	if (params->ret != 0) {
>   		__atomic_store_n(&params->ctrl_thread_status,
> diff --git a/lib/eal/common/malloc_heap.c b/lib/eal/common/malloc_heap.c
> index d7c410b786..3ee19aee15 100644
> --- a/lib/eal/common/malloc_heap.c
> +++ b/lib/eal/common/malloc_heap.c
> @@ -717,6 +717,10 @@ malloc_get_numa_socket(void)
>   			return socket_id;
>   	}
>   
> +	socket_id = rte_lcore_to_socket_id(rte_get_main_lcore());
> +	if (socket_id != (unsigned int)SOCKET_ID_ANY)
> +		return socket_id;
> +
>   	return rte_socket_id_by_idx(0);
>   }
>   

I may be lacking context, but I don't quite get the suggested change. 
 From what I understand, the original has to do with assigning lcore 
cpusets in such a way that an lcore ends up having two socket ID's 
(because it's been assigned to CPU's on different sockets). Why is this 
allowed in the first place? It seems like a user error to me, as it 
breaks many of the fundamental assumptions DPDK makes.

I'm fine with using main lcore socket for control threads, I just don't 
think the `socket_id != SOCKET_ID_ANY` thing should be checked here, 
because it apparently tries to compensate for a problem with cpuset of 
the main thread, which shouldn't have happened to begin with.

-- 
Thanks,
Anatoly