Re: [PATCH v7] enhance NUMA affinity heuristic

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

On 5/23/2023 3:50 AM, Kaisen You wrote:
> When a DPDK application is started on only one numa node, memory is
> allocated for only one socket. When interrupt threads use memory,
> memory may not be found on the socket where the interrupt thread
> is currently located, and memory has to be reallocated on the hugepage,
> this operation will lead to performance degradation.
> 
> Fixes: 705356f0811f ("eal: simplify control thread creation")
> Fixes: 770d41bf3309 ("malloc: fix allocation with unknown socket ID")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Kaisen You <kaisenx.you@intel.com>

Hi You,

I've suggested comment rewordings based on my understanding of the issue.

> ---
> Changes since v6:
> - New explanation for easy understanding,
> 
> Changes since v5:
> - Add comments to the code,
> 
> 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 | 6 ++++++
>   lib/eal/common/malloc_heap.c       | 9 +++++++++
>   2 files changed, 15 insertions(+)
> 
> diff --git a/lib/eal/common/eal_common_thread.c b/lib/eal/common/eal_common_thread.c
> index 079a385630..6479b66da1 100644
> --- a/lib/eal/common/eal_common_thread.c
> +++ b/lib/eal/common/eal_common_thread.c
> @@ -252,6 +252,12 @@ static int ctrl_thread_init(void *arg)
>   	struct rte_thread_ctrl_params *params = arg;
>   
>   	__rte_thread_init(rte_lcore_id(), cpuset);
> +	/* set the value of the per-core variable _socket_id to SOCKET_ID_ANY.
> +	 * Satisfy the judgment condition when threads find memory.
> +	 * If SOCKET_ID_ANY is not specified, the thread may go to a node with
> +	 * unallocated memory in a subsequent memory search.

I suggest a different comment wording:

Set control thread socket ID to SOCKET_ID_ANY as control threads may be 
scheduled on any NUMA node.

> +	 */
> +	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 d25bdc98f9..6d37f8afee 100644
> --- a/lib/eal/common/malloc_heap.c
> +++ b/lib/eal/common/malloc_heap.c
> @@ -716,6 +716,15 @@ malloc_get_numa_socket(void)
>   		if (conf->socket_mem[socket_id] != 0)
>   			return socket_id;
>   	}
> +	/* Trying to allocate memory on the main lcore numa node.
> +	 * especially when the DPDK application is started only on one numa node.
> +	 */

I suggest the following comment wording:

We couldn't find quickly find a NUMA node where memory was available, so 
fall back to using main lcore socket ID.

> +	socket_id = rte_lcore_to_socket_id(rte_get_main_lcore());
> +	/* When the socket_id obtained in the main lcore numa is SOCKET_ID_ANY,
> +	 * The probability of finding memory on rte_socket_id_by_idx(0) is higher.
> +	 */

I suggest the following comment wording:

Main lcore socket ID may be SOCKET_ID_ANY in cases when main lcore 
thread is affinitized to multiple NUMA nodes.

> +	if (socket_id != (unsigned int)SOCKET_ID_ANY)
> +		return socket_id;
>   

I suggest adding comment here:

Failed to find meaningful socket ID, so just use the first one available.

>   	return rte_socket_id_by_idx(0);
>   }

I believe these comments offer better explanation as to why we are doing 
the things we do here.

Whether or not you decide to take these corrections on board,

Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>

-- 
Thanks,
Anatoly