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

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

On 5/18/2020 10:49 PM, Dharmik Thakkar wrote:
> 
> 
>> 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
> 

+1