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

[Alex Kiselev <kiselev99@gmail.com>]

пт, 5 июл. 2019 г. в 13:31, Medvedkin, Vladimir <vladimir.medvedkin@intel.com>:
>
> Hi Stephen,
>
> On 28/06/2019 16:35, Stephen Hemminger wrote:
> > On Fri, 28 Jun 2019 15:16:30 +0100
> > "Medvedkin, Vladimir" <vladimir.medvedkin@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@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@intel.com>
> >>>>>>>> Signed-off-by: Ruifeng Wang<ruifeng.wang@arm.com>
> >>>>>>>> Reviewed-by: Gavin Hu<gavin.hu@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.
>
> You're absolutely right,  control plane performance is mostly depends on
> algorithm. Current LPM implementation has number of problems there. One
> problem is rules_tbl[] that is a flat array containing routes for
> control plane purposes. Replacing it with a rb-tree solves this problem,
> but there are another problems. For example, when you try to add a route
> 10.0.0.0/8 while a number of subroutes are exist in the table (for
> example 10.20.0.0/16), current implementation will load tbl_entry -> do
> some checks (depth, ext entry) -> conditionally store new entry. Under
> several circumstances it would take a lot time.  But in fact it needs to
> unconditionally rewrite only two ranges - from 10.0.0.0 to 10.19.255.255
> and from 10.21.0.0 to 10.255.255.255. And control plane could help us to
> get this two ranges. The best struct to do so is lc-tree because it is
> relatively easy to traverse subtree (described by 10.0.0.0/8) and get
> subroutes. We are working on a new implementation, hopefully it will be
> ready soon.

Have you considered switching to this algorithm?
http://www.nxlab.fer.hr/dxr/

-- 
Alex