Re: [dpdk-dev] L3fwd mode in testpmd

[Jerin Jacob <jerinjacobk@gmail.com>]

On Sat, Apr 24, 2021 at 5:56 AM Honnappa Nagarahalli
<Honnappa.Nagarahalli@arm.com> wrote:
>
> <snip>
>
> > > > > > > > > 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.