[dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port andnbsegments

Morten Brørup mb at smartsharesystems.com
Wed Jul 12 17:57:27 CEST 2017


> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Stephen Hemminger
> Sent: Wednesday, July 12, 2017 5:36 PM
> To: Morten Brørup
> Cc: Yang, Zhiyong; Wiles, Keith; Thomas Monjalon; DPDK; Olivier Matz;
> Wang, Zhihong; Yuanhan Liu; Ananyev, Konstantin; Richardson, Bruce;
> Chilikin, Andrey; Jan Blunck; Nélio Laranjeiro;
> arybchenko at solarflare.com; jerin.jacob at caviumnetworks.com
> Subject: Re: [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port
> andnbsegments
> 
> On Wed, 12 Jul 2017 11:50:38 +0200
> Morten Brørup <mb at smartsharesystems.com> wrote:
> 
> > > -----Original Message-----
> > > From: Yang, Zhiyong [mailto:zhiyong.yang at intel.com]
> > > Sent: Wednesday, July 12, 2017 11:02 AM
> > > To: Morten Brørup; Wiles, Keith
> > > Cc: Thomas Monjalon; DPDK; Olivier Matz; Wang, Zhihong; Yuanhan
> Liu;
> > > Ananyev, Konstantin; Richardson, Bruce; Chilikin, Andrey; Jan
> > > Blunck; Nélio Laranjeiro; arybchenko at solarflare.com;
> > > jerin.jacob at caviumnetworks.com
> > > Subject: RE: [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port
> > > andnbsegments
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Morten
> Brørup
> > > > Sent: Wednesday, July 12, 2017 3:25 PM
> > > > To: Wiles, Keith <keith.wiles at intel.com>
> > > > Cc: Thomas Monjalon <thomas at monjalon.net>; DPDK <dev at dpdk.org>;
> > > > Olivier Matz <olivier.matz at 6wind.com>; Wang, Zhihong
> > > > <zhihong.wang at intel.com>; Yuanhan Liu
> > > > <yuanhan.liu at linux.intel.com>; Ananyev, Konstantin
> > > > <konstantin.ananyev at intel.com>; Richardson, Bruce
> > > > <bruce.richardson at intel.com>; Chilikin, Andrey
> > > > <andrey.chilikin at intel.com>; Jan Blunck <jblunck at infradead.org>;
> > > Nélio
> > > > Laranjeiro <nelio.laranjeiro at 6wind.com>;
> > > > arybchenko at solarflare.com; jerin.jacob at caviumnetworks.com
> > > > Subject: Re: [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port
> > > > and nbsegments
> > > >
> > > > > -----Original Message-----
> > > > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Wiles,
> > > > > Keith
> > > > > Sent: Tuesday, July 11, 2017 6:48 PM
> > > > > To: Morten Brørup
> > > > > Cc: Thomas Monjalon; DPDK; Olivier Matz; Wang, Zhihong; Yuanhan
> > > Liu;
> > > > > Ananyev, Konstantin; Richardson, Bruce; Chilikin, Andrey; Jan
> > > > > Blunck; Nélio Laranjeiro; arybchenko at solarflare.com;
> > > > > jerin.jacob at caviumnetworks.com
> > > > > Subject: Re: [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for
> > > > > port and nbsegments
> > > > >
> > > > >
> > > > > > On Jul 11, 2017, at 10:23 AM, Morten Brørup
> > > > > <mb at smartsharesystems.com> wrote:
> > > > > >
> > > > > >> -----Original Message-----
> > > > > >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Thomas
> > > > > >> Monjalon
> > > > > >> Sent: Tuesday, July 11, 2017 5:06 PM
> > > > > >> To: Morten Brørup
> > > > > >> Cc: dev at dpdk.org; Wiles, Keith; Olivier Matz; Wang, Zhihong;
> > > > > >> Yuanhan Liu; Ananyev, Konstantin; Richardson, Bruce;
> > > > > >> Chilikin, Andrey; Jan Blunck; nelio.laranjeiro at 6wind.com;
> > > > > >> arybchenko at solarflare.com; jerin.jacob at caviumnetworks.com
> > > > > >> Subject: Re: [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for
> > > port
> > > > > and
> > > > > >> nbsegments
> > > > > >>
> > > > > >> 11/07/2017 15:30, Morten Brørup:
> > > > > >>> Morten Brørup wrote:
> > > > > >>>> Olivier Matz wrote:
> > > > > >>>>> As I said in a previous message, I think a good first
> step
> > > > > >>>>> would be to introduce a typedef for the port number:
> > > > > >> rte_eth_port_num_t.
> > > > > >>>>> It can still be uint8_t for now, and can be switched to
> 16
> > > > > >>>>> bits
> > > > > >> in
> > > > > >>>>> one step when everyone uses this new type.
> > > > > >>>>
> > > > > >>>> I think that DPDK follows the Linux tradition of exposing
> > > > > >>>> the variable types, as opposed to hiding them behind
> typedefs.
> > > This
> > > > > has
> > > > > >>>> the unfortunate consequence that when a variable type
> > > > > >>>> changes, it has to be changed everywhere.
> > > > > >>>>
> > > > > >>>> Introducing a rte_eth_port_num_t will require changing the
> > > same
> > > > > >>>> files at the same locations everywhere, so not even as a
> > > > > >>>> temporary solution will it be beneficial.
> > > > > >> [...]
> > > > > >>> What I was trying to communicate with my long argument
> about
> > > > > >>> type
> > > > > >> definitions was: When the type changed from 8 bit to 16 bit,
> > > > > >> the
> > > > > type
> > > > > >> needs to change from uint8_t to uint16_t everywhere too,
> > > > > >> including
> > > > > in
> > > > > >> the ethdev APIs.
> > > > > >>>
> > > > > >>> Don't start breaking coding conventions here by hiding the
> > > > > >>> type of
> > > > > >> this variable.
> > > > > >>
> > > > > >> So, Morten, you are against the typedef, right?
> > > > > >> Because we need to change it everywhere anyway, right?
> > > > > >>
> > > > > >> Note: I have no strong opinion.
> > > > > >
> > > > > > I'm against the typedef because it would break convention,
> and
> > > I'm
> > > > > > a
> > > > > strong proponent of conventions. In other projects, I'm all for
> > > > > typedefs, virtual classes, inheritance etc., but DPDK follows
> > > > > the Linux convention of not hiding simple types.
> > > > > >
> > > > > > We need to change it from uint8_t everywhere, regardless what
> > > > > > we change it to. (But if we need to change it again sometime
> > > > > > in the future, then a typedef will save us next time.)
> > > > >
> > > > > If the number of ports go beyond 64K then I will be the first
> > > > > one (if still alive) to eat this email. :-) The only reason to
> > > > > have
> > > more
> > > > > then
> > > > > 2 bytes would be to encode something into the port id value,
> > > > > which
> > > I
> > > > > could see, but a very slim chance IMHO.
> > > > >
> > > > > >
> > > > > > However, if we change the convention and start hiding simple
> > > > > > types,
> > > > > they still need the rte_ prefix regardless if they are popular
> > > > > or obscure types. Even struct rte_mbuf has the rte_ prefix, and
> > > > > I consider that a very popular type. If so, rte_port_t would be
> > > > > a
> > > good
> > > > > name for this type.
> > > > > >
> > > > > > My preference: Follow convention and change it to uint16_t
> > > > > everywhere.
> > > > > >
> > > > > > Med venlig hilsen / kind regards
> > > > > > - Morten Brørup
> > > > > >
> > > > >
> > > > > As we must change the uint8_t to uint16_t, then I would like it
> > > > > to be more descriptive via a typedef. I really do not see us
> > > > > needing
> > > to
> > > > > change it again in the near future. The only reason to make it
> a
> > > > > typedef is to be able to identify from just the prototype of
> the
> > > > > function that it takes a port ID value, which I am in favor of
> > > doing
> > > > > here for that reason.
> > > >
> > > > That is not a very good reason: When used as a function
> parameter,
> > > the
> > > > type is only shown in the function declaration, whereas the
> > > > variable name is shown every time it is used inside the function.
> > > > So remember to always use meaningful variable names, such as
> > > > "port" (like in the mbuf structure) or "port_id" (used in other
> places).
> > > >
> > > > >
> > > > > As for Olivier’s statement about the typedef name I do not see
> > > > > the need for ‘_eth_' to be part of the typedef as it conveys no
> > > > > extra information in the name. Everything port related in DPDK
> > > > > is a ethernet type device or port. If we do add something like
> > > > > fiber channel maybe rte_pid_t is reason to that too, but if it
> > > > > contains ‘_eth_’ it would not.
> > > > >
> > > > > I would like to see names that are just short enough to convey
> > > > > the information and not be redundant. IMHO rte_pid_t is fine,
> > > > > but if we use some something similar to the length of uint8_t
> > > > > (7) or uint16_t
> > > > > (8) characters then we would not have to also reformat the line
> > > more
> > > > > then needed. Using rte_pid_t (pid == port_id) we only extend
> the
> > > > > length by one (or two) characters and most likely the added
> > > > > byte(s) will not cause more format problems in the code.
> > > >
> > > > I still don't support typedefs for scalar types. I consider it
> > > against
> > > > the coding style, although after reviewing the official DPDK
> > > > Coding Style documentation
> > > > (http://dpdk.org/doc/guides/contributing/coding_style.html), I
> can
> > > see
> > > > that it is not explicitly stated. Please also note that section
> > > > 1.5.7 of the DPDK Coding Style documentation says that the _t
> > > > postfix
> > > should
> > > > be avoided. Anyway, if we end up with a typedef, please don't use
> > > > something resembling pid_t known from POSIX
> > > > (https://www.gnu.org/software/libc/manual/html_node/Process-
> > > > Identification.html).
> > > >
> > >
> > > How about rte_dev_id_t?
> > >
> > > Thanks
> > > Zhiyong
> > >
> > > >
> > > > >
> > > > > Regards,
> > > > > Keith
> >
> > If the DPDK Coding Style is based on Linux Coding Style, we should
> > avoid typedefs in general, not just for structures. Please read Linus
> > Torvalds' opinions about it:
> > http://yarchive.net/comp/linux/typedefs.html
> >
> > Perhaps the DPDK Coding Style should be updated to clarify this. (Or
> > if we decide otherwise, to explicitly mention this deviation from the
> > Linux coding style.)
> 
> It is logical to use typedef's for this kind of scalar type that may
> need to change.
> Names matter, please avoid pid (confuse with posix) and  dev (confuse
> with device id).
> I would prefer: rte_portid_t and rte_queueid_t
> 
> Longer term, probably rte_eth_devices[] needs to go. Change port id
> into something more like ifindex. And use sparse data structure to
> allow very large number of devices and non-contiguous lookup. Think of
> a VPN server where each VPN connection looks like a DPDK device.

We are using a non-contiguous ifindex in our firmware, for virtual interfaces as you mention, so I get your point here! But until DPDK gets there, I suppose the DPDK port id is considered more or less contiguous.

You clearly have a longer track record working with Linus than me, so if you interpret the coding style like that, I will not object anymore - as my objection was based on coding style. And will someone please update the DPDK Coding Style document accordingly...

rte_portid_t is fine with me, but why not just rte_port_t?

PS: uint16_t is a standard C type, not a Linux specific type.


Med venlig hilsen / kind regards
- Morten Brørup



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