[dpdk-dev] [PATCH v3 1/3] lib/lpm: not inline unnecessary functions

[Ruifeng Wang (Arm Technology China)]

Hi Medvedkin,

> -----Original Message-----
> From: Stephen Hemminger <stephen at networkplumber.org>
> Sent: Friday, June 28, 2019 23:35
> To: Medvedkin, Vladimir <vladimir.medvedkin at intel.com>
> Cc: Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; Ruifeng Wang
> (Arm Technology China) <Ruifeng.Wang at arm.com>;
> bruce.richardson at intel.com; dev at dpdk.org; Gavin Hu (Arm Technology
> China) <Gavin.Hu at arm.com>; nd <nd at arm.com>
> Subject: Re: [dpdk-dev] [PATCH v3 1/3] lib/lpm: not inline unnecessary
> functions
> 
> On Fri, 28 Jun 2019 15:16:30 +0100
> "Medvedkin, Vladimir" <vladimir.medvedkin at intel.com> wrote:
> 
> > Hi Honnappa,
> >
> > On 28/06/2019 14:57, Honnappa Nagarahalli wrote:
> > >> Hi all,
> > >>
> > >> On 28/06/2019 05:34, Stephen Hemminger wrote:
> > >>> On Fri, 28 Jun 2019 02:44:54 +0000 "Ruifeng Wang (Arm Technology
> > >>> China)"<Ruifeng.Wang at arm.com>  wrote:
> > >>>
> > >>>>>> Tests showed that the function inlining caused performance drop
> > >>>>>> on some x86 platforms with the memory ordering patches applied.
> > >>>>>> By force no-inline functions, the performance was better than
> > >>>>>> before on x86 and no impact to arm64 platforms.
> > >>>>>>
> > >>>>>> Suggested-by: Medvedkin
> Vladimir<vladimir.medvedkin at intel.com>
> > >>>>>> Signed-off-by: Ruifeng Wang<ruifeng.wang at arm.com>
> > >>>>>> Reviewed-by: Gavin Hu<gavin.hu at arm.com>
> > >>>>>    {
> > >>>>>
> > >>>>> Do you actually need to force noinline or is just taking of inline
> enough?
> > >>>>> In general, letting compiler decide is often best practice.
> > >>>> The force noinline is an optimization for x86 platforms to keep
> > >>>> rte_lpm_add() API performance with memory ordering applied.
> > >>> I don't think you answered my question. What does a recent version
> > >>> of GCC do if you drop the inline.
> > >>>
> > >>> Actually all the functions in rte_lpm should drop inline.
> > >> I'm agree with Stephen. If it is not a fastpath and size of
> > >> function is not minimal it is good to remove inline qualifier for
> > >> other control plane functions such as rule_add/delete/find/etc and
> > >> let the compiler decide to inline it (unless it affects performance).
> > > IMO, the rule needs to be simple. If it is control plane function, we should
> leave it to the compiler to decide. I do not think we need to worry too much
> about performance for control plane functions.
> > Control plane is not as important as data plane speed but it is still
> > important. For lpm we are talking not about initialization, but
> > runtime routes add/del related functions. If it is very slow the
> > library will be totally unusable because after it receives a route
> > update it will be blocked for a long time and route update queue would
> overflow.
> 
> Control plane performance is more impacted by algorithmic choice.
> The original LPM had terrible (n^2?) control path. Current code is better.
> I had a patch using RB tree, but it was rejected because it used the
> /usr/include/bsd/sys/tree.h which added a dependency.

Based on current discussion, I'd like to drop this single patch from the patch set.
Since it is not directly related to memory ordering changes in this library.
We can remove inlines in a follow up patch.