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

[Jesper Dangaard Brouer <brouer@redhat.com>]

On Thu, 17 Nov 2016 20:14:49 -0800 Dave Taht <dave.taht@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.


> I'm going to stop worrying so much about the performance of the new
> wifi algorithms.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer