Hi,
On Sat, Sep 21, 2019 at 04:54:39AM +0000, Wang, Haiyue wrote:
> > -----Original Message-----
> > From: Olivier Matz [mailto:olivier.m...@6wind.com]
> > Sent: Thursday, September 19, 2019 00:55
> > To: dev@dpdk.org
> > Cc: Thomas Monjalon <tho...@monjalon.net>; Wang, Haiyue
> > <haiyue.w...@intel.com>; Stephen Hemminger
> > <step...@networkplumber.org>; Andrew Rybchenko <arybche...@solarflare.com>;
> > Wiles, Keith
> > <keith.wi...@intel.com>; Jerin Jacob Kollanukkaran <jer...@marvell.com>
> > Subject: [PATCH] mbuf: support dynamic fields and flags
> >
> > Many features require to store data inside the mbuf. As the room in mbuf
> > structure is limited, it is not possible to have a field for each
> > feature. Also, changing fields in the mbuf structure can break the API
> > or ABI.
> >
> > This commit addresses these issues, by enabling the dynamic registration
> > of fields or flags:
> >
> > - a dynamic field is a named area in the rte_mbuf structure, with a
> > given size (>= 1 byte) and alignment constraint.
> > - a dynamic flag is a named bit in the rte_mbuf structure.
> >
> > The typical use case is a PMD that registers space for an offload
> > feature, when the application requests to enable this feature. As
> > the space in mbuf is limited, the space should only be reserved if it
> > is going to be used (i.e when the application explicitly asks for it).
> >
> > The registration can be done at any moment, but it is not possible
> > to unregister fields or flags for now.
> >
> > Signed-off-by: Olivier Matz <olivier.m...@6wind.com>
> > Acked-by: Thomas Monjalon <tho...@monjalon.net>
> > ---
> >
> > rfc -> v1
> >
> > * Rebase on top of master
> > * Change registration API to use a structure instead of
> > variables, getting rid of #defines (Stephen's comment)
> > * Update flag registration to use a similar API as fields.
> > * Change max name length from 32 to 64 (sugg. by Thomas)
> > * Enhance API documentation (Haiyue's and Andrew's comments)
> > * Add a debug log at registration
> > * Add some words in release note
> > * Did some performance tests (sugg. by Andrew):
> > On my platform, reading a dynamic field takes ~3 cycles more
> > than a static field, and ~2 cycles more for writing.
> >
> > app/test/test_mbuf.c | 114 ++++++-
> > doc/guides/rel_notes/release_19_11.rst | 7 +
> > lib/librte_mbuf/Makefile | 2 +
> > lib/librte_mbuf/meson.build | 6 +-
> > lib/librte_mbuf/rte_mbuf.h | 25 +-
> > lib/librte_mbuf/rte_mbuf_dyn.c | 408 +++++++++++++++++++++++++
> > lib/librte_mbuf/rte_mbuf_dyn.h | 163 ++++++++++
> > lib/librte_mbuf/rte_mbuf_version.map | 4 +
> > 8 files changed, 724 insertions(+), 5 deletions(-)
> > create mode 100644 lib/librte_mbuf/rte_mbuf_dyn.c
> > create mode 100644 lib/librte_mbuf/rte_mbuf_dyn.h
> >
>
> [snip]
>
> > +/**
> > + * Helper macro to access to a dynamic field.
> > + */
> > +#define RTE_MBUF_DYNFIELD(m, offset, type) ((type)((uintptr_t)(m) +
> > (offset)))
>
> How about to change it as: ?
> #define RTE_MBUF_DYNFIELD(m, offset, type) ((type *)((uintptr_t)(m) +
> (offset)))
> ^
> Then,
> *RTE_MBUF_DYNFIELD(mb, xxx, uint32_t) = yyy;
>
> Since we use 'type' like: sizeof(type), __alignof__(type), this makes 'type'
> be
> more consistent, not have to force cast 'type *' when using it.
>
> const struct rte_mbuf_dynfield dynfield2 = {
> .name = "test-dynfield2",
> .size = sizeof(uint16_t),
> .align = __alignof__(uint16_t),
> .flags = 0,
> };
Yes, I don't see use cases where the '*' is omitted, so it could be in the
macro. On the other hand, doing like in the patch is more consistent with
similar macros like rte_pktmbuf_mtod(), so I'll tend to keep it as is.
This is maybe not that important, because this macro will often be hidden
in a wrapper, like below:
static inline uint64_t rte_mbuf_dyn_timestamp_get(const struct rte_mbuf *m)
{
return *RTE_MBUF_DYNFIELD(m, rte_mbuf_dynfield_timestamp_offset,
uint64_t *);
}
> And also, when I'm trying to use the dynamic flag, found a macro will be
> better
> for making code align with dynamic field. Just a small suggestion. ;-)
> mb->ol_flags |= RTE_MBUF_DYNFLAG(ol_offset);
>
> /**
> * Helper macro to access to a dynamic flag.
> */
> #define RTE_MBUF_DYNFLAG(offset) (1ULL << (offset))
OK, I will add it in next version.
Thank you for the feedback!
Olivier
