From: Stephen Hemminger <stephen@networkplumber.org>
To: Olivier Matz <olivier.matz@6wind.com>
Cc: Jerin Jacob Kollanukkaran <jerinj@marvell.com>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [RFC] mbuf: support dynamic fields and flags
Date: Tue, 16 Jul 2019 07:43:53 -0700 [thread overview]
Message-ID: <20190716074353.66dc910f@hermes.lan> (raw)
In-Reply-To: <20190716093950.kb7w54l2zs3fi7ws@platinum>
On Tue, 16 Jul 2019 11:39:50 +0200
Olivier Matz <olivier.matz@6wind.com> wrote:
> On Fri, Jul 12, 2019 at 12:23:19PM +0000, Jerin Jacob Kollanukkaran wrote:
> > > -----Original Message-----
> > > From: dev <dev-bounces@dpdk.org> On Behalf Of Olivier Matz
> > > Sent: Thursday, July 11, 2019 1:07 PM
> > > To: Stephen Hemminger <stephen@networkplumber.org>
> > > Cc: dev@dpdk.org
> > > Subject: Re: [dpdk-dev] [RFC] mbuf: support dynamic fields and flags
> > >
> > > On Wed, Jul 10, 2019 at 10:49:17AM -0700, Stephen Hemminger wrote:
> > > > On Wed, 10 Jul 2019 11:29:07 +0200
> > > > Olivier Matz <olivier.matz@6wind.com> wrote:
> > > >
> > > > > /**
> > > > > * Indicate that the metadata field in the mbuf is in use.
> > > > > @@ -738,6 +741,8 @@ struct rte_mbuf {
> > > > > */
> > > > > struct rte_mbuf_ext_shared_info *shinfo;
> > > > >
> > > > > + uint64_t dynfield1; /**< Reserved for dynamic fields. */
> > > > > + uint64_t dynfield2; /**< Reserved for dynamic fields. */
> >
> > Since the mbuf size is fixed, What is the downside of union scheme[1] vs upside of proposed scheme
> >
> > [1] Example like:
> > RTE_STD_C11
> > union {
> > void *userdata; /**< Can be used for external metadata */
> > uint64_t udata64; /**< Allow 8-byte userdata on 32-bit */
> > };
>
> In the particular case of userdata, the union is not an issue, it
> just means that there are several ways to represent the same data.
> If needed, it is possible to register a union as a dynamic field.
>
> In other case, like m->hash, having a union makes it impossible to
> use several features of the union at the same time. This would be
> solved by dynamic fields.
>
> > # The fields like mbuf: hash.usr, used in variety of use case together
> > Like libraries like distributor() and Eventdev using it. If we switch
> > to dynamic mbuf scheme, We wil take those field using rte_mbuf_dynfield_register()
> > on library init?
>
> If we decide that these fields must be converted to a dynamic field,
> yes, each library/application will call rte_mbuf_dynfield_register().
>
> > # I see an upside of dynamic mbuf if we can add rte_mbuf_dynfield_unregister API.
> > But can we ever do that? Because it will be complex if we need introduce notification mechanism etc.
>
> An unregister mechanism seems hard to implement, or we can leave the
> hard part to the user: either ensure that no mbuf is in use anywhere, or
> that removing the dynamic field won't have any impact. But I'd prefer
> not introducing an unregistration function until we have a real use-case
> for it.
>
> > # In the real world use case, if with union scheme, fastpath API can simply deference
> > specific element (say mbuf->fieldx). With dynamic scheme, the offset need to store
> > in some other data structure and de reference in fastpath before assessing the interested field.
> > Right?
>
> Yes, with dynamic fields, the offset is stored in a variable. A global
> variable (static to the file or module using it) does the job. This may
> have a small performance impact.
>
Applications are already using userdata reusing that in a driver
would cause a worse disaster than breaking ABI.
next prev parent reply other threads:[~2019-07-16 14:43 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-10 9:29 Olivier Matz
2019-07-10 17:14 ` Wang, Haiyue
2019-07-11 7:26 ` Olivier Matz
2019-07-11 8:04 ` Wang, Haiyue
2019-07-11 8:20 ` Olivier Matz
2019-07-11 8:34 ` Wang, Haiyue
2019-07-11 15:31 ` Stephen Hemminger
2019-07-12 9:18 ` Olivier Matz
2019-07-10 17:49 ` Stephen Hemminger
2019-07-10 18:12 ` Wiles, Keith
2019-07-11 7:53 ` Olivier Matz
2019-07-11 14:37 ` Wiles, Keith
2019-07-12 9:06 ` Olivier Matz
2019-07-11 7:36 ` Olivier Matz
2019-07-12 12:23 ` Jerin Jacob Kollanukkaran
2019-07-16 9:39 ` Olivier Matz
2019-07-16 14:43 ` Stephen Hemminger [this message]
2019-07-11 9:24 ` Thomas Monjalon
2019-07-12 14:54 ` Andrew Rybchenko
2019-07-16 9:49 ` Olivier Matz
2019-07-16 11:31 ` [dpdk-dev] ***Spam*** " Andrew Rybchenko
2019-09-18 16:54 ` [dpdk-dev] [PATCH] " Olivier Matz
2019-09-21 4:54 ` Wang, Haiyue
2019-09-23 8:31 ` Olivier Matz
2019-09-23 11:01 ` Wang, Haiyue
2019-09-21 8:28 ` Wiles, Keith
2019-09-23 8:56 ` Morten Brørup
2019-09-23 9:41 ` Olivier Matz
2019-09-23 9:13 ` Olivier Matz
2019-09-23 15:14 ` Wiles, Keith
2019-09-23 16:16 ` Olivier Matz
2019-09-23 17:14 ` Wiles, Keith
2019-09-23 16:09 ` Wiles, Keith
2019-10-01 10:49 ` Ananyev, Konstantin
2019-10-17 7:54 ` Olivier Matz
2019-10-17 11:58 ` Ananyev, Konstantin
2019-10-17 12:58 ` Olivier Matz
2019-10-17 14:42 ` [dpdk-dev] [PATCH v2] " Olivier Matz
2019-10-18 2:47 ` Wang, Haiyue
2019-10-18 7:53 ` Olivier Matz
2019-10-18 8:28 ` Wang, Haiyue
2019-10-18 9:47 ` Olivier Matz
2019-10-18 11:24 ` Wang, Haiyue
2019-10-22 22:51 ` Ananyev, Konstantin
2019-10-23 3:16 ` Wang, Haiyue
2019-10-23 10:21 ` Olivier Matz
2019-10-23 15:00 ` Stephen Hemminger
2019-10-23 15:12 ` Wang, Haiyue
2019-10-23 10:19 ` Olivier Matz
2019-10-23 11:45 ` Olivier Matz
2019-10-23 11:49 ` Ananyev, Konstantin
2019-10-23 12:00 ` Shahaf Shuler
2019-10-23 13:33 ` Olivier Matz
2019-10-24 4:54 ` Shahaf Shuler
2019-10-24 7:07 ` Olivier Matz
2019-10-24 7:38 ` Slava Ovsiienko
2019-10-24 7:56 ` Olivier Matz
2019-10-24 8:13 ` [dpdk-dev] [PATCH v3] " Olivier Matz
2019-10-24 15:30 ` Stephen Hemminger
2019-10-24 15:44 ` Thomas Monjalon
2019-10-24 17:07 ` Stephen Hemminger
2019-10-24 16:40 ` Thomas Monjalon
2019-10-26 12:39 ` [dpdk-dev] [PATCH v4] " Olivier Matz
2019-10-26 17:04 ` Thomas Monjalon
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