On Sat, Apr 24, 2021 at 5:56 AM Honnappa Nagarahalli
<honnappa.nagaraha...@arm.com> wrote:
>
> <snip>
>
> > > > > > > > > On Thu, Mar 11, 2021 at 12:01 AM Honnappa Nagarahalli
> > > > > > > > > <honnappa.nagaraha...@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.

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