Re: Ethdev tracepoints optimization

[Bruce Richardson <bruce.richardson@intel.com>]

On Thu, Aug 15, 2024 at 03:32:50PM -0400, Adel Belkhiri wrote:
>    Hi DPDK Community,
>    I am currently working on developing performance analyses for
>    applications using the ethdev library. These analyses are being
>    implemented in Trace Compass, an open-source performance analyzer. One
>    of the views I’ve implemented shows the rate of traffic received or
>    sent by an ethernet port, measured in packets per second. However, I've
>    encountered an issue with the lib.ethdev.rx.burst event, which triggers
>    even when no packets are polled, leading to a significant number of
>    irrelevant events in the trace. This becomes problematic as these
>    "empty" events can overwhelm the tracer buffer, potentially causing the
>    loss of more critical events due to their high frequency.
>    To address this, I've modified the DPDK code in lib/ethdev/rte_ethdev.h
>    to add a conditional statement that only triggers the event when nb_rx
>    > 0. My question to the community is whether there are use cases where
>    an "empty" lib.ethdev.rx.burst event could be useful. If not, would
>    there be interest in submitting a patch with this modification?

Yes, there probably would be, but also likely not in such a simple form. I
think there is value in tracing around empty polls too, but only in such a
way not to overflow the trace buffer.

My suggestion would be to trace the first empty poll only, but suppress any
polls thereafter. That way we can know that there are empty polls rather
than no calls.

An even better solution - though I don't know enough about how the tracing
works to know if it's possible - is to match that initial empty poll trace
with some sort of trace output when the empty polls stop, i.e. we get
traffic, recording the number of empty polls received as a count value.

My 2c.

/Bruce