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

["Ruifeng Wang (Arm Technology China)" <Ruifeng.Wang@arm.com>]

> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Sent: Wednesday, September 11, 2019 13:33
> To: Ruifeng Wang (Arm Technology China) <Ruifeng.Wang@arm.com>;
> Ananyev, Konstantin <konstantin.ananyev@intel.com>; Kantecki, Tomasz
> <tomasz.kantecki@intel.com>
> Cc: dev@dpdk.org; Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>;
> nd <nd@arm.com>; nd <nd@arm.com>
> Subject: RE: [dpdk-dev] [PATCH 0/2] add lock-free mode for l3fwd
> 
> > >
> > > <snip>
> > >
> > > > >
> > > > > Hi,
> > > > >
> > > > > >
> > > > > > 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.
> > > >
> > > Without the dynamic deletes the quiescent state reporting overhead
> > > is not captured completely.
> > > I suggest that we add and delete a small set of unrelated routes
> > > (the routes that are not used currently) on a regular basis.
> > >
> > Add and delete unrelated routes on a regular basis will simulate
> > overhead on control path. However, control path performance is not a
> > l3fwd showcase, and it is covered by LPM performance unit test.
> > On data path, quiescent state reporting overhead is constant (calling
> > of rte_rcu_qsbr_quiescent).
> > It will not be impacted by route addition / deletion.
> The recent changes to RCU [1] are such that the reader threads avoid a write
> if there are no deletes. So, without the deletion, the impact on readers is
> complete.
> 
> [1] https://patchwork.dpdk.org/patch/58961/

OK, understand that. 
Assumptions based on current implementation of rte_rcu_qsbr_quiescent is not reliable. 
The part on control path will be added.

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