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From: David Marchand <david.marchand@redhat.com>
Date: Wed, 28 Feb 2024 15:18:40 +0100
Message-ID: <CAJFAV8xF+Bt0DReeX69CJcg6WMxYvcU+SVJskFnBzdAGn9ckYw@mail.gmail.com>
Subject: Re: [PATCH v6 20/23] mbuf: remove and stop using rte marker fields
To: Tyler Retzlaff <roretzla@linux.microsoft.com>
Cc: dev@dpdk.org, Ajit Khaparde <ajit.khaparde@broadcom.com>,
Andrew Boyer <andrew.boyer@amd.com>,
Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>,
Bruce Richardson <bruce.richardson@intel.com>, Chenbo Xia <chenbox@nvidia.com>,
Chengwen Feng <fengchengwen@huawei.com>,
Dariusz Sosnowski <dsosnowski@nvidia.com>,
David Christensen <drc@linux.vnet.ibm.com>, Hyong Youb Kim <hyonkim@cisco.com>,
Jerin Jacob <jerinj@marvell.com>, Jie Hai <haijie1@huawei.com>,
Jingjing Wu <jingjing.wu@intel.com>, John Daley <johndale@cisco.com>,
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Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>,
Maciej Czekaj <mczekaj@marvell.com>,
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Ruifeng Wang <ruifeng.wang@arm.com>, Satha Rao <skoteshwar@marvell.com>,
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Yisen Zhuang <yisen.zhuang@huawei.com>, Yuying Zhang <Yuying.Zhang@intel.com>,
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On Tue, Feb 27, 2024 at 6:44=E2=80=AFAM Tyler Retzlaff
<roretzla@linux.microsoft.com> wrote:
>
> RTE_MARKER typedefs are a GCC extension unsupported by MSVC. Remove
> RTE_MARKER fields from rte_mbuf struct.
>
> Maintain alignment of fields after removed cacheline1 marker by placing
> C11 alignas(RTE_CACHE_LINE_MIN_SIZE).
>
> Update implementation of rte_mbuf_prefetch_part1() and
> rte_mbuf_prefetch_part2() inline functions calculate pointer for
> prefetch of cachline0 and cachline1 without using removed markers.
>
> Update static_assert of rte_mbuf struct fields to reference data_off and
> packet_type fields that occupy the original offsets of the marker
> fields.
>
> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> ---
> doc/guides/rel_notes/release_24_03.rst | 9 ++++++++
> lib/mbuf/rte_mbuf.h | 4 ++--
> lib/mbuf/rte_mbuf_core.h | 39 +++++++++++++---------------=
------
> 3 files changed, 26 insertions(+), 26 deletions(-)
>
> diff --git a/doc/guides/rel_notes/release_24_03.rst b/doc/guides/rel_note=
s/release_24_03.rst
> index 879bb49..67750f2 100644
> --- a/doc/guides/rel_notes/release_24_03.rst
> +++ b/doc/guides/rel_notes/release_24_03.rst
> @@ -156,6 +156,15 @@ Removed Items
> The application reserved statically defined logtypes ``RTE_LOGTYPE_USE=
R1..RTE_LOGTYPE_USER8``
> are still defined.
>
> +* mbuf: ``RTE_MARKER`` fields ``cacheline0`` ``cacheline1``
> + ``rx_descriptor_fields1`` and ``RTE_MARKER64`` field ``rearm_data``
> + have been removed from ``struct rte_mbuf``.
> + Prefetch of ``cacheline0`` and ``cacheline1`` may be achieved through
> + ``rte_mbuf_prefetch_part1()`` and ``rte_mbuf_prefetch_part2()`` inline
> + functions respectively.
> + Access to ``rearm_data`` and ``rx_descriptor_fields1`` should be
> + through new inline functions ``rte_mbuf_rearm_data()`` and
> + ``rte_mbuf_rx_descriptor_fields1()`` respectively.
>
> API Changes
> -----------
> diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
> index aa7495b..61cda20 100644
> --- a/lib/mbuf/rte_mbuf.h
> +++ b/lib/mbuf/rte_mbuf.h
> @@ -108,7 +108,7 @@
> static inline void
> rte_mbuf_prefetch_part1(struct rte_mbuf *m)
> {
> - rte_prefetch0(&m->cacheline0);
> + rte_prefetch0(m);
> }
>
> /**
> @@ -126,7 +126,7 @@
> rte_mbuf_prefetch_part2(struct rte_mbuf *m)
> {
> #if RTE_CACHE_LINE_SIZE =3D=3D 64
> - rte_prefetch0(&m->cacheline1);
> + rte_prefetch0(RTE_PTR_ADD(m, RTE_CACHE_LINE_MIN_SIZE));
> #else
> RTE_SET_USED(m);
> #endif
> diff --git a/lib/mbuf/rte_mbuf_core.h b/lib/mbuf/rte_mbuf_core.h
> index 36551c2..4e06f15 100644
> --- a/lib/mbuf/rte_mbuf_core.h
> +++ b/lib/mbuf/rte_mbuf_core.h
> @@ -18,6 +18,7 @@
>
> #include <assert.h>
> #include <stddef.h>
> +#include <stdalign.h>
> #include <stdint.h>
>
> #include <rte_common.h>
> @@ -467,8 +468,6 @@ enum {
> * The generic rte_mbuf, containing a packet mbuf.
> */
> struct rte_mbuf {
> - RTE_MARKER cacheline0;
> -
> void *buf_addr; /**< Virtual address of segment buffer.=
*/
> #if RTE_IOVA_IN_MBUF
> /**
> @@ -495,7 +494,6 @@ struct rte_mbuf {
> * To obtain a pointer to rearm_data use the rte_mbuf_rearm_data(=
)
> * accessor instead of directly referencing through the data_off =
field.
> */
> - RTE_MARKER64 rearm_data;
> uint16_t data_off;
One subtile change of removing the marker is that fields may not be
aligned as before.
#if RTE_IOVA_IN_MBUF
/**
* Physical address of segment buffer.
* This field is undefined if the build is configured to use only
* virtual address as IOVA (i.e. RTE_IOVA_IN_MBUF is 0).
* Force alignment to 8-bytes, so as to ensure we have the exact
* same mbuf cacheline0 layout for 32-bit and 64-bit. This makes
* working on vector drivers easier.
*/
rte_iova_t buf_iova __rte_aligned(sizeof(rte_iova_t));
#else
/**
* Next segment of scattered packet.
* This field is valid when physical address field is undefined.
* Otherwise next pointer in the second cache line will be used.
*/
struct rte_mbuf *next;
#endif
When building ! RTE_IOVA_IN_MBUF on a 32 bits arch, the next pointer
is not force aligned to 64bits.
Which has a cascade effect on data_off alignement.
In file included from ../lib/mbuf/rte_mbuf_core.h:19,
from ../lib/mbuf/rte_mbuf.h:42,
from ../lib/mbuf/rte_mbuf_dyn.c:18:
../lib/mbuf/rte_mbuf_core.h:676:1: error: static assertion failed: "data_of=
f"
676 | static_assert(!(offsetof(struct rte_mbuf, data_off) !=3D
| ^~~~~~~~~~~~~
I hope reviewers pay attention to the alignment changes when removing
those markers.
This is not trivial to catch in the CI.
--=20
David Marchand