Re: [dpdk-dev] [PATCH v2] mbuf: support dynamic fields and flags

["Wang, Haiyue" <haiyue.wang@intel.com>]

> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Wednesday, October 23, 2019 06:52
> To: Olivier Matz <olivier.matz@6wind.com>; dev@dpdk.org
> Cc: Andrew Rybchenko <arybchenko@solarflare.com>; Richardson, Bruce <bruce.richardson@intel.com>; Wang,
> Haiyue <haiyue.wang@intel.com>; Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Wiles, Keith
> <keith.wiles@intel.com>; Morten Brørup <mb@smartsharesystems.com>; Stephen Hemminger
> <stephen@networkplumber.org>; Thomas Monjalon <thomas@monjalon.net>
> Subject: RE: [PATCH v2] 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.matz@6wind.com>
> > Acked-by: Thomas Monjalon <thomas@monjalon.net>
> > ---
> >
> > v2
> >
> > * Rebase on top of master: solve conflict with Stephen's patchset
> >   (packet copy)
> > * Add new apis to register a dynamic field/flag at a specific place
> > * Add a dump function (sugg by David)
> > * Enhance field registration function to select the best offset, keeping
> >   large aligned zones as much as possible (sugg by Konstantin)
> > * Use a size_t and unsigned int instead of int when relevant
> >   (sugg by Konstantin)
> > * Use "uint64_t dynfield1[2]" in mbuf instead of 2 uint64_t fields
> >   (sugg by Konstantin)
> > * Remove unused argument in private function (sugg by Konstantin)
> > * Fix and simplify locking (sugg by Konstantin)
> > * Fix minor typo
> >
> > 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                   | 145 ++++++-
> >  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             |  23 +-
> >  lib/librte_mbuf/rte_mbuf_dyn.c         | 548 +++++++++++++++++++++++++
> >  lib/librte_mbuf/rte_mbuf_dyn.h         | 226 ++++++++++
> >  lib/librte_mbuf/rte_mbuf_version.map   |   7 +
> >  8 files changed, 959 insertions(+), 5 deletions(-)
> >  create mode 100644 lib/librte_mbuf/rte_mbuf_dyn.c
> >  create mode 100644 lib/librte_mbuf/rte_mbuf_dyn.h
> >
> > diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
> > index b9c2b2500..01cafad59 100644
> > --- a/app/test/test_mbuf.c
> > +++ b/app/test/test_mbuf.c
> > @@ -28,6 +28,7 @@
> >  #include <rte_random.h>
> >  #include <rte_cycles.h>
> >  #include <rte_malloc.h>
> > +#include <rte_mbuf_dyn.h>
> >

[snip]
> > +int
> > +rte_mbuf_dynflag_register_bitnum(const struct rte_mbuf_dynflag *params,
> > +				unsigned int req)
> > +{
> > +	int ret;
> > +
> > +	if (req != UINT_MAX && req >= 64) {
> 
> Might be better to replace 64 with something like sizeof(mbuf->ol_flags) * CHAR_BIT or so.

Might introduce a new macro like kernel:

/**
 * FIELD_SIZEOF - get the size of a struct's field
 * @t: the target struct
 * @f: the target struct's field
 * Return: the size of @f in the struct definition without having a
 * declared instance of @t.
 */
#define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))

Then: FIELD_SIZEOF(rte_mbuf, ol_flags) * CHAR_BIT

> Apart from that:
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> 
> > +		rte_errno = EINVAL;
> > +		return -1;
> > +	}
> > +
> > +	rte_mcfg_tailq_write_lock();
> > +	ret = __rte_mbuf_dynflag_register_bitnum(params, req);
> > +	rte_mcfg_tailq_write_unlock();
> > +
> > +	return ret;
> > +}
> > +