linux-kernel - Re: [PATCH net-next v9 7/9] libeth: add Rx buffer management

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Date: Fri, 5 Apr 2024 12:32:55 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
CC: Alexander Duyck <alexanderduyck@...com>, Yunsheng Lin
	<linyunsheng@...wei.com>, Jesper Dangaard Brouer <hawk@...nel.org>, "Ilias
 Apalodimas" <ilias.apalodimas@...aro.org>, Christoph Lameter <cl@...ux.com>,
	Vlastimil Babka <vbabka@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
	<nex.sw.ncis.osdt.itp.upstreaming@...el.com>, <netdev@...r.kernel.org>,
	<intel-wired-lan@...ts.osuosl.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v9 7/9] libeth: add Rx buffer management

On 4/4/24 17:44, Alexander Lobakin wrote:
> Add a couple intuitive helpers to hide Rx buffer implementation details
> in the library and not multiplicate it between drivers. The settings are
> sorta optimized for 100G+ NICs, but nothing really HW-specific here.
> Use the new page_pool_dev_alloc() to dynamically switch between
> split-page and full-page modes depending on MTU, page size, required
> headroom etc. For example, on x86_64 with the default driver settings
> each page is shared between 2 buffers. Turning on XDP (not in this
> series) -> increasing headroom requirement pushes truesize out of 2048
> boundary, leading to that each buffer starts getting a full page.
> The "ceiling" limit is %PAGE_SIZE, as only order-0 pages are used to
> avoid compound overhead. For the above architecture, this means maximum
> linear frame size of 3712 w/o XDP.
> Not that &libeth_buf_queue is not a complete queue/ring structure for
> now, rather a shim, but eventually the libeth-enabled drivers will move
> to it, with iavf being the first one.
> 
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> ---
>   drivers/net/ethernet/intel/libeth/Kconfig |   1 +
>   include/net/libeth/rx.h                   | 117 ++++++++++++++++++++++
>   drivers/net/ethernet/intel/libeth/rx.c    |  98 ++++++++++++++++++
>   3 files changed, 216 insertions(+)
>
[...]

> +/**
> + * struct libeth_fqe - structure representing an Rx buffer
> + * @page: page holding the buffer
> + * @offset: offset from the page start (to the headroom)
> + * @truesize: total space occupied by the buffer (w/ headroom and tailroom)
> + *
> + * Depending on the MTU, API switches between one-page-per-frame and shared
> + * page model (to conserve memory on bigger-page platforms). In case of the
> + * former, @offset is always 0 and @truesize is always ```PAGE_SIZE```.
> + */
> +struct libeth_fqe {
> +	struct page		*page;
> +	u32			offset;
> +	u32			truesize;
> +} __aligned_largest;
> +
> +/**
> + * struct libeth_fq - structure representing a buffer queue
> + * @fp: hotpath part of the structure
> + * @pp: &page_pool for buffer management
> + * @fqes: array of Rx buffers
> + * @truesize: size to allocate per buffer, w/overhead
> + * @count: number of descriptors/buffers the queue has
> + * @buf_len: HW-writeable length per each buffer
> + * @nid: ID of the closest NUMA node with memory
> + */
> +struct libeth_fq {
> +	struct_group_tagged(libeth_fq_fp, fp,
> +		struct page_pool	*pp;
> +		struct libeth_fqe	*fqes;
> +
> +		u32			truesize;
> +		u32			count;
> +	);
> +
> +	/* Cold fields */
> +	u32			buf_len;
> +	int			nid;
> +};

[...]

Could you please unpack the meaning of `fq` and `fqe` acronyms here?

otherwise the whole series is very good for me, thank you very much!