Re: [dpdk-dev] L3fwd mode in testpmd

[Thomas Monjalon <thomas@monjalon.net>]

27/04/2021 11:57, Ananyev, Konstantin:
> From: Yigit, Ferruh <ferruh.yigit@intel.com>
> > On 4/26/2021 9:46 PM, Honnappa Nagarahalli wrote:
> > >>>>>>>>>>>> On Thu, Mar 11, 2021 at 12:01 AM Honnappa
> > >>>>>>>>>>>> Nagarahalli <Honnappa.Nagarahalli@arm.com> wrote:
> > >>>>>>>>>>>>>
> > >>>>>>>>>>>>> Hello,
> > >>>>>>>>>>>>>         Performance of L3fwd example application
> > >>>>>>>>>>>>> is one of the key
> > >>>>>>>>>>>> benchmarks in DPDK. However, the application does
> > >>>>>>>>>>>> not have many debugging statistics to understand the
> > >>>>>>>>>>>> performance issues. We have added L3fwd as another
> > >>>>>>>>>>>> mode/stream to testpmd which provides
> > >>>>>>>>>> enough
> > >>>>>>>>>>>> statistics at various levels. This has allowed us to
> > >>>>>>>>>>>> debug the performance issues effectively.
> > >>>>>>>>>>>>>
> > >>>>>>>>>>>>> There is more work to be done to get it to
> > >>>>>>>>>>>>> upstreamable state. I am
> > >>>>>>>>>>>> wondering if such a patch is helpful for others and
> > >>>>>>>>>>>> if the community would be interested in taking a
> > >>>>>>>>>>>> look. Please let me know
> > >>>>>>>>> what you think.
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> We are using app/proc-info/ to attach and analyze
> > >>>>>>>>>>>> the
> > >>>>> performance.
> > >>>>>>>>>>>> That helps to analyze the unmodified application. I
> > >>>>>>>>>>>> think, if something is missing in proc-info app, in
> > >>>>>>>>>>>> my opinion it is better to enhance proc-info so that
> > >>>>>>>>>>>> it can help other third-party
> > >>>>>>> applications.
> > >>>>>>>>>>>>
> > >>>>>>>>>>>> Just my 2c.
> > >>>>>>>>>>> Thanks Jerin. We will explore that.
> > >>>>>>>>>>
> > >>>>>>>>>> I agree it is dangerous to rely too much on testpmd for
> > >> everything.
> > >>>>>>>>>> Please tell us what in testpmd could be useful out of it.
> > >>>>>>>>>>
> > >>>>>>>>> Things that are very helpful in testpmd are: 1) HW
> > >>>>>>>>> statistics from the NIC 2) Forwarding stats 3) Burst stats
> > >>>>>>>>> (indication of headroom
> > >>>>>>>>> availability) 4) Easy to set parameters like RX and TX
> > >>>>>>>>> queue depths (among others) without having to recompile.
> > >>>>>>>>
> > >>>>>>>> [Kathleen Capella]
> > >>>>>>>> Thank you for the suggestion of app/proc-info. I've tried it
> > >>>>>>>> out with l3fwd and see that it does have the HW stats from
> > >>>>>>>> the NIC and the forwarding
> > >>>>>>> stats.
> > >>>>>>>> However, it does not have the burst stats testpmd offers,
> > >>>>>>>> nor the
> > >>>>>>>
> > >>>>>>> One option to see such  level of debugging would be to have
> > >>>>>>> - Create a memzone in the primary process
> > >>>>>>> - Application under test can update the stats in memzone based
> > >>>>>>> on the code flow
> > >>>>>>> - proc-info can read the counters updated by application under
> > >>>>>>> test using the memzone object got through
> > >> rte_memzone_lookup()
> > >>>>>> Agreed. Currently, using app/proc-info does not provide this
> > >>>>>> ability. We
> > >>>>> cannot add this capability to app/proc-info as these stats would
> > >>>>> be specific to L3fwd application.
> > >>>>>
> > >>>>> I meant creating generic counter-read/write infra via memzone to
> > >>>>> not make it as l3fwd specific.
> > >>>> Currently, app/proc-info is able to print the stats as they are standardized
> > >> via the API. But for statistics that are generated in the application, they are
> > >> very specific to that application. For ex: burst stats in testpmd are very
> > >> specific to it and another application might implement the same in a very
> > >> different manner.
> > >>>>
> > >>>> In needs to be something like the app/proc-info just needs to be a dumb
> > >> displaying utility and the application has to do all the heavy lifting of copying
> > >> the exact display strings to the memory.
> > >>>
> > >>> Yes.
> > >>>
> > >>>>
> > >>>>>>>
> > >>>>>>> Another approach will be using rte_trace()[1] for
> > >>>>>>> debugging/tracing by adding tracepoints in l3fwd for such events.
> > >>>>>>> It has a timestamp and the trace format is opensource trace
> > >>>>>>> format(CTF(Common trace format)), so that we can use post
> > >>>>>>> posting tools to analyze.
> > >>>>>>> [1]
> > >>>>>>> https://doc.dpdk.org/guides/prog_guide/trace_lib.html
> > >>>>>> This is good for analyzing an incident. I think it is an
> > >>>>>> overhead for
> > >>>>> development purposes.
> > >>>>>
> > >>>>> Consider if one wants to add burst stats, one can add stats
> > >>>>> increment under RTE_TRACE_POINT_FP, it will be emitted whenever
> > >>>>> code flow through that path. Set of events of can be viewed in
> > >>>>> trace viewer[1]. Would that be enough?
> > >>>>> Adding traces to l3fwd can be upstreamed as it is useful for
> > >>>>> others for debugging.
> > >>>>>
> > >>>>> [1]
> > >>>>> https://github.com/jerinjacobk/share/blob/master/dpdk_trace.JPG
> > >>>> This needs post processing of the trace info to derive the information, is it
> > >> correct? For ex: for burst stats, there will be several traces generated
> > >> collecting the number of packets returned by rte_eth_rx_burst which needs
> > >> to be post processed.
> > >>>
> > >>> Or You can have an additional variable to acculate it.
> > >>>
> > >>>> Also, adding traces is equivalent to adding statistics in L3fwd.
> > >>>
> > >>> Yes.
> > >>>
> > >>> If the sole purpose only stats then it is better to add status in
> > >>> l3fwd without performance impact. I thought some thing else.
> > >>>
> > >>>>
> > >>>>>>>
> > >>>>>>>> ability to easily change parameters without having to
> > >>>>>>>> recompile, which helps reduce debugging time significantly.
> > >>>> We will not be able to fix this above issue.
> > >>>
> > >>> It depends on what you want to debug. Trace can be disabled at runtime.
> > >>
> > >>
> > >> DPDK has existing API's for application metrics but they are rarely used.
> > >>
> > >> Why not implement rte_metrics in l3fwd and proc-info?
> > > This discussion has ended up as a stats discussion. But, we also need to be able to change the configurable parameters easily.
> > > If we implement the stats and ability to change the configurable parameters, then it is essentially bringing in some of the capabilities from
> > testpmd to the sample application. I think that will result in lot more code in the sample application and will make it complicated.
> > >
> > > Instead our proposal is to take L3fwd to testpmd and use all the infra code that testpmd provides. We see that this approach results in less
> > amount of code added to DPDK overall.
> > >
> > 
> > Agree that it may help testing to have l3fwd support on the testpmd.
> > 
> > Two concerns,
> > 1) Testpmd already too complex.
> > 2) Code duplication.
> > 
> > For 1), if the l3fwd can be implemented in testpmd as new, independent
> > forwarding mode, without touching rest of the testpmd, I think it can be OK.
> 
> In fact, l3fwd is also quite big and complex:
> $ wc -l examples/l3fwd/*.[h,c] |grep total
>   6969 total
> 
> Plus it will introduce extra dependencies (fib, lpm, hash, might-be acl?)
> I am not sure it is a good idea to pull all these complexities into test-pmd.
> I can't imagine that l3fwd app need ability to configure each and every
> PMD parameter.
> From my experience in l3fwd most of cycles are spent not in PMD itself,
> but in actual packet processing: header parsing and checking, classification,
> routing table lookup, etc. 

testpmd goal is to test the driver, not the libraries.
 
> > Not sure how to address 2), also lets say we want to add new feature to l3fwd,
> > where it should go, to the sample or to the testpmd?

l3fwd is not targetted for testing.

Maybe we just lack a new test application for routing libraries?