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

[Dharmik Thakkar <Dharmik.Thakkar@arm.com>]

> On May 18, 2020, at 4:47 AM, Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> 
> On 5/15/2020 9:33 PM, Dharmik Thakkar wrote:
>> Hi Ferruh,
>> 
>>> On May 15, 2020, at 7:15 AM, Ferruh Yigit <ferruh.yigit@intel.com> wrote:
>>> 
>>> 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
>> 
>> CPU cycles/packet shown above is a part of the example. The numbers are as per the statistics shown in the example.
> 
> I know but now you are showing a performance number and it is specific to a
> platform, my concern it may be misleading and create false expectations for others.

Ok, makes sense.

> 
>> 
>>> 
>>>> +
>>>> +.. note::
>>>> +
>>>> +   Measuring CPU cycles/packet requires enabling CONFIG_RTE_TEST_PMD_RECORD_CORE_TX_CYCLES
>>> 
>>> s/TX_CYCLES/CYCLES
>> 
>> Sorry, didn’t understand this comment.
> 
> There is no 'CONFIG_RTE_TEST_PMD_RECORD_CORE_TX_CYCLES' config option.

Got it, will update.

> 
>> 
>>> 
>>>> +   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.
>> 
>> This additional comment about aarch64 platforms is to provide complete information to the users with regards to the config option
>> and offer a better understanding of the CPU cycles/packet numbers. IMO, without this note, CPU cycles/packet numbers can be misleading.
> 
> This is testpmd documentation to describe "show fwd stats" command. We are
> adding a note to say with a config option it may also show performance data,
> which is OK. But starting to describe the platform differences for this config
> option looks to much details for the scope of the document. For testpmd I would
> prefer command usage independent from platforms, otherwise the documentation may
> become too confusing/complex.
> But agree to provide the information for the specific platform, which you are
> already doing in other patch in the platform documentation.

Alright, I will remove platform in the next version.

> 
>> 
>>> 
>>> 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
>>> "
>> 
>> Yes, this is also an option. IMO, numbers shown within CPU cycles/packet example should be consistent with the forward statistics numbers.
>> 
> 
> This part is just the sample of the "CPU cycles/packet" output, I think it
> provides enough context to be understandable without matching Rx packet count in
> above part of the stats.

Instead of adding 2 samples, do you think using xxx is best? For example:
CPU cycles/packet=xx.dd (total cycles=xxxx / total RX packets=xxxx) at xxxx MHz clock