Re: [dpdk-dev] [PATCH 0/2] add lock-free mode for l3fwd

[Ruifeng Wang (Arm Technology China)]

> -----Original Message-----
> From: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> Sent: Wednesday, September 11, 2019 13:38
> To: Ruifeng Wang (Arm Technology China) <ruifeng.w...@arm.com>;
> Ananyev, Konstantin <konstantin.anan...@intel.com>; Kantecki, Tomasz
> <tomasz.kante...@intel.com>
> Cc: dev@dpdk.org; Gavin Hu (Arm Technology China) <gavin...@arm.com>;
> Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>; nd
> <n...@arm.com>; nd <n...@arm.com>
> Subject: RE: [dpdk-dev] [PATCH 0/2] add lock-free mode for l3fwd
> 
> <snip>
> > >
> > >
> > >
> > > > >
> > > > > >
> > > > > > Lock-free mode is supported by hash library and LPM library.
> > > > > > Now we add an option for l3fwd example to enable the lock-free
> > mode.
> > > > > > Necessary preparation steps are added to use lock-free LPM mode.
> > > > >
> > > > > Can I ask about the purpose of these changes?
> > > > > Right now in  l3fwd both lpm and hash tables are static and hard-
> coded.
> > > > > we initialize them at startup and then just do read from them.
> > > > > Do you plan to enhance l3fwd with ability to dynamically update
> > > > > tables contents?
> > > > > Though fir that we first have to get rid of hard-coded values
> > > > > (config file or
> > > so).
> > > > > Konstantin
> > > > >
> > > > Thanks for your questions.
> > > > Currently, we have no plan to enhance l3fwd with ability to
> > > > dynamically
> > > update table contents.
> > > > Lock-free method is being integrated into Hash library and LPM
> > > > library.  Lock-free algorithms are not only about control plane
> > > > (adding or deleting routes), they affect the data path performance as
> well.
> > > > Since l3fwd application is showcasing data path performance, we
> > > > need to show the impact of including the quiescent state reporting
> > > > on data
> > path.
> > > > This change also serves as an example of using the RCU APIs.
> > >
> > >
> > > But what you suggest doesn't provide the complete picture.
> > > With dynamic updates in place (via control path) the data-path
> > > impact might be completely different then without.
> > > Again without dynamic updates how can you test that your data-path
> > > lock- free approach does work as expected?
> > > Also it can't even be used as a reference implementation for users,
> > > as half of the functionality they need to implement is simply missing.
> > > My opinion - we either need to leave l3fwd as it is (static routes),
> > > or implement a proper control path with ability to dynamically
> > > update routes before starting to introduce some synchronization
> > > schemes (RCU or whatever).
> > >
> > > Konstantin
> > >
> >
> > Agree that dynamic control path updates should be included for a whole
> > picture.
> > I will add dynamic update to l3fwd and reroll the patch series.
> > Thanks.
> I think we should have an agreement on what exactly we mean by
> 'dynamically update routes'.
> IMO, we should not disturb the existing static routes as there might be
> automated tests running in the labs. I suggest that we should add/delete
> new routes/hash entries which are different from the existing routes/hash
> entries. This should be sufficient to showcase the functionality as well as
> measure the impact.
> 
Yes, existing static routes should be kept intact.
To perform regular route/hash entries add/delete, a dedicated lcore will be 
needed.
An interactive prompt is not an option since we need automatic add/delete.
We can skip master core for data path main loop. And perform unrelated 
route/hash entries add/delete regularly on master core.
The impact is that command lines used in tests will need update since master 
core will no longer do data path work.
> >
> > > >
> > > > > >
> > > > > > Patch 2/2 has dependency on RCU QSBR integration with LPM
> library:
> > > > > > http://patches.dpdk.org/project/dpdk/list/?series=6288
> > > > > >
> > > > > >
> > > > > > Ruifeng Wang (2):
> > > > > >   examples/l3fwd: add lock-free option for l3fwd
> > > > > >   examples/l3fwd: integrate RCU QSBR for LPM mode
> > > > > >
> > > > > >  doc/guides/sample_app_ug/l3_forward.rst |  3 ++
> > > > > >  examples/l3fwd/Makefile                 |  1 +
> > > > > >  examples/l3fwd/l3fwd.h                  |  4 +-
> > > > > >  examples/l3fwd/l3fwd_em.c               | 10 +++-
> > > > > >  examples/l3fwd/l3fwd_lpm.c              | 72
> > > +++++++++++++++++++++++--
> > > > > >  examples/l3fwd/main.c                   | 27 ++++++++--
> > > > > >  examples/l3fwd/meson.build              |  1 +
> > > > > >  7 files changed, 108 insertions(+), 10 deletions(-)
> > > > > >
> > > > > > --
> > > > > > 2.17.1
> >
>