Re: [dpdk-dev] [PATCH 2/2] fib: announce experimental tag removal of the fib API

[Jan Viktorin <viktorin@cesnet.cz>]

On Thu, 5 Aug 2021 16:29:50 +0200
"Medvedkin, Vladimir" <vladimir.medvedkin@intel.com> wrote:

> On 05/08/2021 16:07, Jan Viktorin wrote:
> > On Thu, 5 Aug 2021 15:57:14 +0200
> > "Medvedkin, Vladimir" <vladimir.medvedkin@intel.com> wrote:
> >   
> >> On 05/08/2021 15:32, Jan Viktorin wrote:  
> >>> On Thu, 5 Aug 2021 15:27:15 +0200
> >>> "Medvedkin, Vladimir" <vladimir.medvedkin@intel.com> wrote:
> >>>      
> >>>> Hi Jan,
> >>>>
> >>>> The RIB is always used as a control plane struct intended to
> >>>> maintain the correct content of the dataplane struct, such as
> >>>> DIR24_8 for example. So it is always used on _add()/_delete().
> >>>> For simplicity you can consider it as an LPM's rule_info. But
> >>>> instead of keeping routes in a plane array as it is in LPM, FIB
> >>>> uses RIB which is more suitable binary tree.  
> >>>
> >>> OK. I thought that I can have a single RIB, use it for maintaining
> >>> routes and based on this single RIB, I can build a FIB for the
> >>> data plane. And when the single RIB is updated (which can take
> >>> quite a lot of time) I build a new FIB and locklessly give it to
> >>> the dataplane. Such approach is not considered?
> >>>
> >>> Jan
> >>>      
> >>
> >> I'm not sure I understood completely your use case. Do you want to
> >> rebuild the entire FIB from scratch every time the RIB changes?  
> > 
> > The idea was to maintain a single RIB and two FIBs. One FIB is
> > active and under heavy load and when a route change arrives, it is
> > first written to RIB. When RIB is ready, it is used to quickly
> > construct/update the second inactive FIB. Then I swap with the
> > current active FIB. The old one can be edited/updated/recreated and
> > new one is active.
> > 
> > I've got one place where all routes are placed (RIB). And two FIBs
> > that contain only routes that are relevant. (Well, yes, not all
> > routes in RIB might be relevant, this depends on other conditions.)
> > 
> > Jan
> >   
> 
> This technique is used for data structures that do not support 
> incremental updates. However FIB supports incremental updates.
> 
> You can keep a separate rib struct and reflect changes to the fib.

But reflecting the changes is sometimes really more difficult than just
rebuilding from scratch.

> 
> Also, using rte_fib_get_rib() you can get the corresponding RIB
> struct and work with it directly using rib API. However you need to

But than I've got two RIBs that I have to keep in sync with each other
which is quite difficult.

> be cautious, all adding/deletion and next hop changing must be done
> using fib API.

Because, otherwise the DIR24_8 is not in sync, right?

Jan

> 
> >>  
> >>>>
> >>>>
> >>>> On 05/08/2021 15:14, Jan Viktorin wrote:  
> >>>>> On Thu, 5 Aug 2021 15:08:13 +0200
> >>>>> Vladimir Medvedkin <vladimir.medvedkin@intel.com> wrote:
> >>>>>         
> >>>>>> This patch announces the experimental tag removal of all fib
> >>>>>> APIs, which have been experimental for 2 years.
> >>>>>> API will be promoted to stable in DPDK 21.11  
> >>>>>
> >>>>> Hi Vladimir,
> >>>>>
> >>>>> I have a question related to FIB. I am just learning how to use
> >>>>> it and I found that each FIB always creates a new RIB
> >>>>> internally. There is no doc about this topic...
> >>>>>
> >>>>> If I understand correctly, the underlying RIB is only used when
> >>>>> dummy_lookup() and dummy_modify() are used. But they are only
> >>>>> used when the configured mode is RTE_FIB_DUMMY. Is there any
> >>>>> reason to create the RIB with RTE_FIB_DIR24_8?
> >>>>>
> >>>>> The issue with this is that each RIB allocates a new mempool
> >>>>> internally which can waste quite a lot of never used memory that
> >>>>> would be unused with DIR24_8 implementation.
> >>>>>
> >>>>> Regards
> >>>>> Jan
> >>>>>         
> >>>>>>
> >>>>>>
> >>>>>> Signed-off-by: Vladimir Medvedkin
> >>>>>> <vladimir.medved...@intel.com> ---
> >>>>>>     doc/guides/rel_notes/deprecation.rst | 2 ++
> >>>>>>     1 file changed, 2 insertions(+)
> >>>>>>
> >>>>>> diff --git a/doc/guides/rel_notes/deprecation.rst
> >>>>>> b/doc/guides/rel_notes/deprecation.rst
> >>>>>> index afb599a..58826a8 100644
> >>>>>> --- a/doc/guides/rel_notes/deprecation.rst
> >>>>>> +++ b/doc/guides/rel_notes/deprecation.rst
> >>>>>> @@ -195,3 +195,5 @@ Deprecation Notices
> >>>>>>       communicate events such as soft expiry with IPsec in
> >>>>>> lookaside mode.
> >>>>>>     * rib: The ``rib`` library will be promoted from
> >>>>>> experimental to stable. +
> >>>>>> +* fib: The ``fib`` library will be promoted from experimental
> >>>>>> to stable.  
> >>>>     
> >>>      
> >>  
> >   
>