Re: [dpdk-dev] [PATCH v2 3/5] doc: add cycles per packet in testpmd user guide

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 5/8/2020 11:38 PM, Dharmik Thakkar wrote:
> Update documentation for 'show fwd' testpmd runtime function to show
> CPU cycles/packet example.
> 
> Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Phil Yang <phil.yang@arm.com>
> ---
> v2:
>  - Use shorter lines, up to 100.
> ---
>  doc/guides/testpmd_app_ug/testpmd_funcs.rst | 53 +++++++++++++--------
>  1 file changed, 33 insertions(+), 20 deletions(-)
> 
> diff --git a/doc/guides/testpmd_app_ug/testpmd_funcs.rst b/doc/guides/testpmd_app_ug/testpmd_funcs.rst
> index a360ecccfd3f..441ed41e3803 100644
> --- a/doc/guides/testpmd_app_ug/testpmd_funcs.rst
> +++ b/doc/guides/testpmd_app_ug/testpmd_funcs.rst
> @@ -351,26 +351,39 @@ Example for the io forwarding engine, with some packet drops on the tx side::
>  
>     testpmd> show fwd stats all
>  
> -     ------- Forward Stats for RX Port= 0/Queue= 0 -> TX Port= 1/Queue= 0 -------
> -     RX-packets: 274293770      TX-packets: 274293642      TX-dropped: 128
> -
> -     ------- Forward Stats for RX Port= 1/Queue= 0 -> TX Port= 0/Queue= 0 -------
> -     RX-packets: 274301850      TX-packets: 274301850      TX-dropped: 0
> -
> -     ---------------------- Forward statistics for port 0  ----------------------
> -     RX-packets: 274293802      RX-dropped: 0             RX-total: 274293802
> -     TX-packets: 274301862      TX-dropped: 0             TX-total: 274301862
> -     ----------------------------------------------------------------------------
> -
> -     ---------------------- Forward statistics for port 1  ----------------------
> -     RX-packets: 274301894      RX-dropped: 0             RX-total: 274301894
> -     TX-packets: 274293706      TX-dropped: 128           TX-total: 274293834
> -     ----------------------------------------------------------------------------
> -
> -     +++++++++++++++ Accumulated forward statistics for all ports+++++++++++++++
> -     RX-packets: 548595696      RX-dropped: 0             RX-total: 548595696
> -     TX-packets: 548595568      TX-dropped: 128           TX-total: 548595696
> -     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> +     ------- Forward Stats for RX Port= 0/Queue= 0 -> TX Port= 1/Queue= 0 -------
> +     RX-packets: 43536504       TX-packets: 43536488       TX-dropped: 0
> +
> +     ------- Forward Stats for RX Port= 1/Queue= 0 -> TX Port= 0/Queue= 0 -------
> +     RX-packets: 149738504      TX-packets: 149738504      TX-dropped: 0
> +
> +     ------- Forward Stats for RX Port= 1/Queue= 1 -> TX Port= 0/Queue= 1 -------
> +     RX-packets: 149753052      TX-packets: 149753052      TX-dropped: 0
> +
> +     ---------------------- Forward statistics for port 0  ----------------------
> +     RX-packets: 43538881       RX-dropped: 72            RX-total: 43538953
> +     TX-packets: 299491753      TX-dropped: 0             TX-total: 299491753
> +     ----------------------------------------------------------------------------
> +
> +     ---------------------- Forward statistics for port 1  ----------------------
> +     RX-packets: 299493085      RX-dropped: 8357          RX-total: 299501442
> +     TX-packets: 43539683       TX-dropped: 0             TX-total: 43539683
> +     ----------------------------------------------------------------------------
> +
> +     +++++++++++++++ Accumulated forward statistics for all ports+++++++++++++++
> +     RX-packets: 343031966      RX-dropped: 8429          RX-total: 343040395
> +     TX-packets: 343031436      TX-dropped: 0             TX-total: 343031436
> +     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> +
> +     CPU cycles/packet=14.28 (total cycles=4899533541 / total RX packets=343031966) at 200 MHz Clock

Hi Dharmik,

Overall it is OK to show "CPU cycles/packet", but my concern is numbers can be
misleading, because for example the numbers I am getting is like below:

CPU cycles/packet=4.38 (total cycles=32871036274 / total RX packets=7511734336)
at 2100 MHz Clock

> +
> +.. note::
> +
> +   Measuring CPU cycles/packet requires enabling CONFIG_RTE_TEST_PMD_RECORD_CORE_TX_CYCLES

s/TX_CYCLES/CYCLES

> +   configuration option. On aarch64 platforms, by default, the cycles are counted using
> +   generic counter which runs at a lower frequency than the CPU clock. To get the cycles/packet
> +   at CPU clock frequency, please scale the cycles/packet to CPU clock frequency.
> +   Alternatively, use the PMU based cycle counter.

Not sure the "aarch64 platforms" note suits to here, where documents the
command. And I can see the platform documentation already updated for this.

Combining above two comments, what do you think instead of replacing existing
stats, add a note saying enabling 'CONFIG_RTE_TEST_PMD_RECORD_CORE_CYCLES'
appends "CPU cycles/packet" and give above two samples, like:

"
Enabling RTE_TEST_PMD_RECORD_CORE_CYCLES appends "CPU cycles/packet" stats, like:

CPU cycles/packet=4.38 (total cycles=32871036274 / total RX packets=7511734336)
at 2100 MHz Clock
OR
CPU cycles/packet=14.28 (total cycles=4899533541 / total RX packets=343031966)
at 200 MHz Clock
"