Throughput & CPU usage of WiFi download

[Marc Gonzalez]

Hello everyone,

I've been benchmarking various aspects of an SEI530 board,
and wanted to share some of the results with the list.

The main objective was to compare WiFi download performance
on mainline/BR2 and vendor/android systems.

(Mainline system was generated using pop-br2-ext-tree.zip.
brcmfmac4359-sdio.* left out for size.)


HW spec
Board: SEI530 (SEI510 variant)
SoC: S905X2
WiFi: AP6398SR3-J (SDIO BCM4359/9)

Test setup
WiFi AP using 5Ghz channels 120 (primary) + 116 (secondary)
BENCHMARK = "curl --silent -o /dev/null http://192.168.1.254:8095/fixed/10G"
Kernel booted with
1) performance governor (no DVFS)
2) nohlt (keep counting cycles in idle)


(Full results at the end)

Observations:
- vendor system manages 245 Mbps, using 40% CPU
- mainline system manages 60 Mbps, using 10% CPU
- vendor system limited to 62 Mbps, uses 9% CPU

1) Neil Armstrong mentioned that vendor kernel reaches
higher throughput by playing tricks with some pads?
(Not sure I understood that well, haven't looked at the code)

2) SDIO is clocked higher on vendor system, but could
lead to instabilities on some boards?

Interesting possible followups
- try clocking SDIO higher on mainline system
- measure CPU usage at 120 Mbps, does it scale linearly to 20%?
- android curl seems to use smaller buffers?


TEST RESULTS

-- mainline/BR2 (v6.2)

time perf record -a -F 1009 $BENCHMARK
perf report -s pid -n --header

10_GB in 1338.127552_s = 59.8_Mbps

# Overhead       Samples      Pid:Command
  90.0445%       4863024        0:swapper = IDLE
   7.2362%        390807       56:irq/17-ffe03000
   1.9282%        104136       59:kworker/u9:0-br
   0.6965%         37616      142:curl
   0.0722%          3897      114:ksdioirqd/mmc2
   0.0168%           908      141:perf


-- vendor/android (4.9.180 + vendor patches)

time simpleperf record -a -f 1009 $BENCHMARK
simpleperf report --sort pid,comm

10_GB in 326.54_s = 245_Mbps

Overhead  Sample  Pid    Command
59.43%    680339  0      swapper = IDLE
12.59%    156593  15378  curl
11.42%    136024  4392   dhd_rxf
7.57%     88047   4391   dhd_dpc
2.52%     29977   2094   irq/51-meson-am
1.38%     16467   10541  system_server
0.75%     10394   17     ksoftirqd/1
0.73%     9282    15377  simpleperf
0.60%     9226    6      ksoftirqd/0
0.38%     4701    14865  kworker/0:0
0.14%     2055    29     ksoftirqd/3
0.13%     1636    3411   HwBinder:3411_1
0.13%     1760    23     ksoftirqd/2
0.12%     1484    10782  dmx_data_thread
0.12%     1469    3381   composer at 2.3-se
0.10%     1329    15425  Jit thread pool


Same benchmark, rate limited to 8 MB/s
time simpleperf record -a -f 1009 $BENCHMARK --limit-rate 8M
simpleperf report --sort pid,comm

10_GB in 1290.22_s = 62 Mbps

Overhead  Sample   Pid    Command
91.68%    3687632  0      swapper = IDLE
2.67%     107057   4392   dhd_rxf
1.90%     74721    4391   dhd_dpc
1.00%     41650    22975  curl
0.70%     29239    10541  system_server
0.68%     27406    2094   irq/51-meson-am
0.58%     24781    22974  simpleperf
0.10%     4222     17     ksoftirqd/1
0.10%     4070     10782  dmx_data_thread
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