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From: Jerin Jacob <jerinjacobk@gmail.com>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: dpdk-dev <dev@dpdk.org>,
	David Marchand <david.marchand@redhat.com>,
	 Olivier Matz <olivier.matz@6wind.com>,
	Jerin Jacob <jerinj@marvell.com>,
	 Nithin Dabilpuram <ndabilpuram@marvell.com>,
	Krzysztof Kanas <kkanas@marvell.com>,
	 Andrew Rybchenko <arybchenko@solarflare.com>,
	Ferruh Yigit <ferruh.yigit@intel.com>,
	 "Richardson, Bruce" <bruce.richardson@intel.com>,
	John McNamara <john.mcnamara@intel.com>,
	 Marko Kovacevic <marko.kovacevic@intel.com>
Subject: Re: [dpdk-dev] [PATCH] mbuf: document rule for new fields and flags
Date: Tue, 26 May 2020 13:09:37 +0530
Message-ID: <CALBAE1MTmsO=_N3Ui2SY_z57k6gKpPORVLZ4EwaZ9vpHRHXomg@mail.gmail.com> (raw)
In-Reply-To: <20200525212415.3173817-1-thomas@monjalon.net>

On Tue, May 26, 2020 at 2:54 AM Thomas Monjalon <thomas@monjalon.net> wrote:
>
> Since dynamic fields and flags were added in 19.11,
> the idea was to use them for new features, not only PMD-specific.
>
> The rule is made more explicit in doxygen, in the mbuf guide,
> and in the contribution design guidelines.
>
> For more information about the original design, see the presentation
> https://www.dpdk.org/wp-content/uploads/sites/35/2019/10/DynamicMbuf.pdf
>
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> ---
>  doc/guides/contributing/design.rst | 13 +++++++++++++
>  doc/guides/prog_guide/mbuf_lib.rst | 23 +++++++++++++++++++++++
>  lib/librte_mbuf/rte_mbuf_core.h    |  2 ++
>  3 files changed, 38 insertions(+)
>
> diff --git a/doc/guides/contributing/design.rst b/doc/guides/contributing/design.rst
> index d3dd694b65..508115d5bd 100644
> --- a/doc/guides/contributing/design.rst
> +++ b/doc/guides/contributing/design.rst
> @@ -57,6 +57,19 @@ The following config options can be used:
>  * ``CONFIG_RTE_EXEC_ENV`` is a string that contains the name of the executive environment.
>  * ``CONFIG_RTE_EXEC_ENV_FREEBSD`` or ``CONFIG_RTE_EXEC_ENV_LINUX`` are defined only if we are building for this execution environment.
>
> +Mbuf features
> +-------------
> +
> +The ``rte_mbuf`` structure must be kept small (128 bytes).
> +
> +In order to add new features without wasting buffer space for unused features,
> +some fields and flags can be registered dynamically in a shared area.

I think, instead of "can", it should be "must"

> +The "dynamic" mbuf area is the default choice for the new features.
> +
> +The "dynamic" area is eating the remaining space in mbuf,
> +and some existing "static" fields may need to become "dynamic".
> +
> +
>  Library Statistics
>  ------------------
>
> diff --git a/doc/guides/prog_guide/mbuf_lib.rst b/doc/guides/prog_guide/mbuf_lib.rst
> index 0d3223b081..c3dbfb9221 100644
> --- a/doc/guides/prog_guide/mbuf_lib.rst
> +++ b/doc/guides/prog_guide/mbuf_lib.rst
> @@ -207,6 +207,29 @@ The list of flags and their precise meaning is described in the mbuf API
>  documentation (rte_mbuf.h). Also refer to the testpmd source code
>  (specifically the csumonly.c file) for details.
>
> +Dynamic fields and flags
> +~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +The size of the mbuf is constrained and limited;
> +while the amount of metadata to save for each packet is quite unlimited.
> +The most basic networking information already find their place
> +in the existing mbuf fields and flags.
> +
> +If new features need to be added, the new fields and flags should fit

How about, instead of "should fit", must use the dynamic space.

> +in the "dynamic space", by registering some room in the mbuf structure:
> +
> +dynamic field
> +   named area in the mbuf structure,
> +   with a given size (at least 1 byte) and alignment constraint.
> +
> +dynamic flag
> +   named bit in the mbuf structure,
> +   stored in the field ``ol_flags``.
> +
> +The dynamic fields and flags are managed with the functions ``rte_mbuf_dyn*``.
> +
> +It is not possible to unregister fields or flags.
> +
>  .. _direct_indirect_buffer:
>
>  Direct and Indirect Buffers
> diff --git a/lib/librte_mbuf/rte_mbuf_core.h b/lib/librte_mbuf/rte_mbuf_core.h
> index b9a59c879c..22be41e520 100644
> --- a/lib/librte_mbuf/rte_mbuf_core.h
> +++ b/lib/librte_mbuf/rte_mbuf_core.h
> @@ -12,6 +12,8 @@
>   * packet offload flags and some related macros.
>   * For majority of DPDK entities, it is not recommended to include
>   * this file directly, use include <rte_mbuf.h> instead.
> + *
> + * New fields and flags should fit in the "dynamic space".

must use.

>   */
>
>  #include <stdint.h>
> --
> 2.26.2
>

  reply	other threads:[~2020-05-26  7:39 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-25 21:24 Thomas Monjalon
2020-05-26  7:39 ` Jerin Jacob [this message]
2020-05-26 16:06   ` Olivier Matz
2020-05-26 16:29     ` Jerin Jacob
2020-05-27  7:09       ` Olivier Matz
2020-05-27  7:31         ` Jerin Jacob
2020-05-27  9:51           ` Thomas Monjalon
2020-05-27 11:43             ` Jerin Jacob
2020-05-27 11:56               ` Thomas Monjalon
2020-05-27 12:07                 ` Jerin Jacob
2020-05-27 12:23                   ` Olivier Matz
2020-05-27 12:34                     ` Jerin Jacob
2020-06-11  6:32 ` [dpdk-dev] [PATCH v2] mbuf: document guideline " Thomas Monjalon
2020-06-11  6:37   ` Jerin Jacob
2020-06-11  7:30     ` Thomas Monjalon

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