On Wed, Feb 28, 2024 at 4:01 PM Morten Brørup <m...@smartsharesystems.com> wrote: > > > From: David Marchand [mailto:david.march...@redhat.com] > > Sent: Wednesday, 28 February 2024 15.19 > > > > On Tue, Feb 27, 2024 at 6:44 AM Tyler Retzlaff > > <roret...@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 <roret...@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_notes/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_USER1..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 == 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_off" > > 676 | static_assert(!(offsetof(struct rte_mbuf, data_off) != > > | ^~~~~~~~~~~~~ > > > > > > I hope reviewers pay attention to the alignment changes when removing > > those markers. > > This is not trivial to catch in the CI. > > Good catch, David. > > I wonder about the reason for 64 bit aligning the rearm_data group of fields? > Perhaps it's there for (64 bit arch) vector instruction purposes? > > Regardless, it's an ABI break, so padding or an alignment attribute must be > added to avoid ABI breakage. If there is no valid reason for the 64 bit > alignment, it could be noted that the padding (or alignment attribute) is > there for 32 bit arch ABI compatibility reasons only. > > Please note that only RTE_MARKER64 is affected by this. The other marker > types have arch bit-width (or smaller) alignment, i.e. RTE_MARKER is 8 byte > aligned on 64 bit arch and 4 byte aligned on 32 bit arch.
Well, strictly speaking other RTE_MARKER users *may* be affected, depending on the alignement for the following fields. For example, I think removing the rxq_fastpath_data_end RTE_MARKER in struct nicvf_rxq (https://git.dpdk.org/dpdk/tree/drivers/net/thunderx/nicvf_struct.h#n72) impacts rx_drop_en alignment and subsequent fields. Now, in practice and focusing only on what this series touches, either the markers were coupled with an explicit alignment constraint (__rte_cache*_aligned) which is preserved by the series, or the alignement constraint is stronger than that of the marker. So there is probably only this ABI breakage I reported. -- David Marchand
