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

Ananyev, Konstantin konstantin.ananyev at intel.com
Wed Sep 11 10:35:15 CEST 2019



> -----Original Message-----
> From: Ruifeng Wang (Arm Technology China) [mailto:Ruifeng.Wang at arm.com]
> Sent: Wednesday, September 11, 2019 7:58 AM
> To: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; Ananyev, Konstantin <konstantin.ananyev at intel.com>; Kantecki, Tomasz
> <tomasz.kantecki at intel.com>
> Cc: dev at dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>; nd <nd at arm.com>; nd <nd at arm.com>; nd <nd at arm.com>
> Subject: RE: [dpdk-dev] [PATCH 0/2] add lock-free mode for l3fwd
> 
> > -----Original Message-----
> > From: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>
> > Sent: Wednesday, September 11, 2019 13:38
> > To: Ruifeng Wang (Arm Technology China) <Ruifeng.Wang at arm.com>;
> > Ananyev, Konstantin <konstantin.ananyev at intel.com>; Kantecki, Tomasz
> > <tomasz.kantecki at intel.com>
> > Cc: dev at dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>;
> > Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; nd
> > <nd at arm.com>; nd <nd at 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.

Not sure why it has to be  master core?
Why interrupt thread wouldn't do?
I think what we need to:
1. introduce reading routes from config file instead of having them hard-coded within the app.
2. add ability to update routes dynamically.
    Probably the easiest (and commonly used way) re-read conf file and update routes on the signal (SIGUSR1 or so).
Konstantin


> > >
> > > > >
> > > > > > >
> > > > > > > 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
> > >
> >



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