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From:   Jesper Dangaard Brouer <jbrouer@redhat.com>
Message-ID: <1af55bbb-7aff-e575-8dc1-8ba64b924580@redhat.com>
Date:   Mon, 24 Jul 2023 13:29:28 +0200
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        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
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Subject: Re: [PATCH V3,net-next] net: mana: Add page pool for RX buffers
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To:     Haiyang Zhang <haiyangz@microsoft.com>,
        linux-hyperv@vger.kernel.org, netdev@vger.kernel.org
References: <1689966321-17337-1-git-send-email-haiyangz@microsoft.com>
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On 21/07/2023 21.05, Haiyang Zhang wrote:
> Add page pool for RX buffers for faster buffer cycle and reduce CPU
> usage.
> 
> The standard page pool API is used.
> 
> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> ---
> V3:
> Update xdp mem model, pool param, alloc as suggested by Jakub Kicinski
> V2:
> Use the standard page pool API as suggested by Jesper Dangaard Brouer
> 
> ---
>   drivers/net/ethernet/microsoft/mana/mana_en.c | 91 +++++++++++++++----
>   include/net/mana/mana.h                       |  3 +
>   2 files changed, 78 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
> index a499e460594b..4307f25f8c7a 100644
> --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
[...]
> @@ -1659,6 +1679,8 @@ static void mana_poll_rx_cq(struct mana_cq *cq)
>   
>   	if (rxq->xdp_flush)
>   		xdp_do_flush();
> +
> +	page_pool_nid_changed(rxq->page_pool, numa_mem_id());

I don't think this page_pool_nid_changed() called is needed, if you do
as I suggest below (nid = NUMA_NO_NODE).


>   }
>   
>   static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
[...]

> @@ -2008,6 +2041,25 @@ static int mana_push_wqe(struct mana_rxq *rxq)
>   	return 0;
>   }
>   
> +static int mana_create_page_pool(struct mana_rxq *rxq)
> +{
> +	struct page_pool_params pprm = {};

You are implicitly assigning NUMA node id zero.

> +	int ret;
> +
> +	pprm.pool_size = RX_BUFFERS_PER_QUEUE;
> +	pprm.napi = &rxq->rx_cq.napi;

You likely want to assign pprm.nid to NUMA_NO_NODE

  pprm.nid = NUMA_NO_NODE;

For most drivers it is recommended to assign ``NUMA_NO_NODE`` (value -1)
as the NUMA ID to ``pp_params.nid``. When ``CONFIG_NUMA`` is enabled
this setting will automatically select the (preferred) NUMA node (via
``numa_mem_id()``) based on where NAPI RX-processing is currently
running. The effect is that page_pool will only use recycled memory when
NUMA node match running CPU. This assumes CPU refilling driver RX-ring
will also run RX-NAPI.

If a driver want more control over the NUMA node memory selection,
drivers can assign (``pp_params.nid``) something else than
`NUMA_NO_NODE`` and runtime adjust via function ``page_pool_nid_changed()``.

I will update [1] with this info.
  - Docs [1] 
https://kernel.org/doc/html/latest/networking/page_pool.html#registration


> +
> +	rxq->page_pool = page_pool_create(&pprm);
> +
> +	if (IS_ERR(rxq->page_pool)) {
> +		ret = PTR_ERR(rxq->page_pool);
> +		rxq->page_pool = NULL;
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +