[Make-wifi-fast] a bit of profiling on the archer

[Toke Høiland-Jørgensen]

Jesper Dangaard Brouer <brouer at redhat.com> writes:

> On Thu, 17 Nov 2016 20:14:49 -0800 Dave Taht <dave.taht at gmail.com> wrote:
>
>> I have not been profiling much on lower end platforms (it's hard, you
>> can crash a box pretty easily with the wrong options or sample rates).
>
> I'm happy to hear that perf does work on this lower end HW, although
> the disclaimer of sample rates.
>
> Does anyone know if hardware based PMU (Performance Monitor Units)
> exists for these kind of devices?
>
>> While watching the ath10k peak at 150-200mbits, at 99% of cpu in
>> softirq, I spent a bit of time profiling various counters and
>> statistics.
>> 
>> for this one (while downloading 12 flows at the same time via flent)
>> 
>> perf record -F 99 -e cpu-clock -ag -- sleep 10
>> 
>> perf report
>
> Below perf report is not well suite for email, could you instead
> provide output from command below:
>
> perf report --no-children --stdio --call-graph none
>
>>
>>   [[31m  67.81%[[m     0.00%  ksoftirqd/0  [kernel.kallsyms]       [k]
>> run_ksoftirqd
>>             |
>>             ---run_ksoftirqd
>>                |
>>                |[[31m--67.61%-- [[m __do_softirq
>>                |          |
>>                |          |[[31m--66.80%-- [[m net_rx_action
>>                |          |          |
>>                |          |          |[[31m--41.07%-- [[m ag71xx_poll
>> 
>> ...
>
> (Looks like you managed to copy-paste the terminal escape codes for
> colors)
>
>> 
>> It appears we're spending 66% of the time in the *ethernet* portion of
>> the path.
>
> Be careful you don't fool yourself. In your output you have the
> "children" mode on, so everything being called "under" net_rx_action is
> summed up.  It could be it goes all the way through to the wifi TX
> parts and that is part of the sum.  Even the memory allocations gets
> summed into this 66% number.

Yes, actually my guess would be that this is the case. When I was
profiling ath9k I saw this exact behaviour.

-Toke