Raspberry Pi Zero data transfer rate test
The Raspberry Pi stores the images which are collected during flight. After the plane landed, the images are retrieved from the Pi. The least impact with respect to water sealing would be a wireless transfer via Wifi or Bluetooth. For completeness I also test the transfer rate via USB configured as RNDIS network device. As a seperate topic I look into the transfer rate of the SD Card.
Author: Friedrich Beckmann
Raspberry Pi configuration
I did a headless setup and connected the Pi via USB to startup the pi.
- Download the Raspbian SD Card image from raspberrypi.org
- Install Etcher (on MacOS) and download the image to the SD Card
- Setup the Pi for Headless connection via USB according to this description
In order to be able to login via ssh over usb cable, the following modifications have to be done on the SD Card. All changes are done in the files in the root folder. That folder is formatted FAT32 and can be accessed and modified via MacOS.
config.txt
Append at the bottom of config.txt
dtoverlay=dwc2
cmdline.txt
After rootwait, append
modules-load=dwc2,g_ether
and only add one space between and no newline. The parsing of this line is delicate.
Enable SSH
ssh is disabled by default. In order to be able to login via ssh, the ssh service has to be enabled in the Pi. This can be done by creating an empty file on the SD Card.
Create an empty file “ssh”
That file is deleted every time the pi does a new boot. So if you power off the pi, then you need to create that file again to be able to login via ssh.
Boot the Pi
Attach the Pi via the USB cable to the Mac. There are two USB connectors on the Pi. You must attach the cable to the connector labeled “USB”. Do not attach it to the connector labeled “PWR” - that connector does not provide a data connection. No additional power supply is required. The Pi is powered from the Macbook.
When the Pi boots, the green LED blinks when the SDCARD is accessed. Once boot is finished, the green LED stays on permanently.
Setup on the Mac
Go to System Preferences/Network or Systemeinstellungen/Netzwerk and check if you find RNDIS/Ethernet Gadget. That is the Raspberry Pi which is connected as network device. Then you can login to the Pi. Open a terminal on the Mac and do
ssh pi@raspberrypi.local
The default user on the Pi is pi and the default password is raspberry.
Enable ssh permanently
You need to enable ssh access permanenty with
sudo ssh systemctl enable ssh
Configure a static IP address for Raspberry Pi
The default behavior of the Pi RNDIS service is to receive an IP address vi dhcp. But the Mac does not provide a DHCP service, so we configure the Pi to have the fixed IP address 192.168.2.2. The Mac is setup to have the IP address 192.168.2.1. To configure the pi append to
/etc/dhcpcd.conf
interface usb0 static ip_address=192.168.2.2/24 static routers=192.168.2.1 static domain_name_servers=192.168.2.1
On the Mac go to Systemeinstellungen/Netzwerk. You need to configure the IP setup for the “RNDIS/Ethernet Gadget” device to “manual”. Set the IP to 192.168.2.1 and the subnetmask to “255.255.255.0”.
Configure the MAC to provide internet access to the Pi
As default the Pi is connected locally to the Mac. To provide internet access to the Pi via the Mac go to Systemeinstellungen/Freigaben and activate Internetfreigabe for RNDIS/Ethernet Gadget.
To check the internet access on the Pi open a terminal on the Mac and login to the pi via ssh. Then check
ping www.hs-augsburg.de
on the Pi. You should get a connection the hs-augsburg web server.
Setup WLAN access as wlan client
To setup the Pi to connect to the WLAN access point as client, I modified the file
/etc/wpa_supplicant/wpa_supplicant.conf
country=DE
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid="fred"
scan_ssid=1
psk="dosenpups"
key_mgmt=WPA-PSK
}
You can also place that file in the root folder on the Pi from the Mac. That will result in copying the wpa_supplicant.conf file the the /etc/wpa_supplicant directory and start the Wifi service. I am not too sure if this is permant or only for one boot.
Data transfer via Wifi / USB
Measurement Setup
The Raspberry is connected as WLAN client to the Fritzbox 7390 as access point. The Raspberry Pi Zero only has a 2.4 GHz rf modem and can not connect in the 5 GHz band. The Pi Zero W uses the CYW43438 chipset with 802.11n in single mimo stream setup and a maximum bandwidth of 20 MHz. This setup limits the air rate of the Pi to 65 MBit/s for a standard guard interval of 800ns and 72 MBit/s for a short guard interval. The Macbook is connected via Wifi to a Apple Timecapsule in the 5 GHz band, i.e. the Macbook is connected via seperate band to the FritzBox access point an does not use the channel bandwidth. There are no other clients connected to the Fritzbox AP. The channel is however occupied by other 2.4 GHz stations in the neighbourhood.
- Raspberry Pi Zero WH
- SanDisk Edge 8 GB - Class4 U1 SDHC Card
- Raspbian Buster Lite release from 2019-09-26 with kernel 4.19
- Macbook Pro (Retina 13 inch, Modell 2015) running MacOS 10.13.6 High Sierra
- Fritzbox 7390 as WLAN access point for the Raspberry Pi in 2.4 GHz band
- Apple Timecapsule 3GB version 7.9.1 for the 5 GHZ Wifi connection of the Mac
The Fritzbox reports the Raspberry Pi connection status with 65 MBit/s when I place the Pi in about 1m distance to the AP. There is no possibility to configure the FritzBox for Short Guard Interval, i.e. the system runs with the default 800ns GI.
Install iperf on the Raspberry Pi
To install iperf on Raspberry Pi run
sudo apt install iperf
Install iperf in the Mac
I installed iperf version 2.0.5 via homebrew. So on the Mac
brew install iperf
iperf data transfer rate measurement via USB
The iperf datastream goes from the client to the server. For our scenario the relevant direction is Pi to Mac. Therefore I run the iperf server on the Mac and the client on the Pi. iperf opens a tcp connection from the client to the server.
On the Mac
iperf -s
On the Pi
iperf -i 10 -t 300 -c 192.168.2.1
That tests the TCP/IP data transfer speed from the Pi to the Mac via USB connection. Each test interval is 10s and the toal test time is 300s. The result looks like this:
pi@raspberrypi:~ $ iperf -i 10 -t 300 -c 192.168.2.1 ------------------------------------------------------------ Client connecting to 192.168.2.1, TCP port 5001 TCP window size: 70.0 KByte (default) ------------------------------------------------------------ [ 3] local 192.168.2.2 port 34428 connected with 192.168.2.1 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 185 MBytes 155 Mbits/sec [ 3] 10.0-20.0 sec 186 MBytes 156 Mbits/sec [ 3] 20.0-30.0 sec 186 MBytes 156 Mbits/sec [ 3] 30.0-40.0 sec 186 MBytes 156 Mbits/sec [ 3] 40.0-50.0 sec 185 MBytes 155 Mbits/sec [ 3] 50.0-60.0 sec 180 MBytes 151 Mbits/sec [ 3] 60.0-70.0 sec 180 MBytes 151 Mbits/sec [ 3] 70.0-80.0 sec 180 MBytes 151 Mbits/sec [ 3] 80.0-90.0 sec 181 MBytes 152 Mbits/sec [ 3] 90.0-100.0 sec 181 MBytes 152 Mbits/sec [ 3] 100.0-110.0 sec 181 MBytes 152 Mbits/sec [ 3] 110.0-120.0 sec 184 MBytes 155 Mbits/sec [ 3] 120.0-130.0 sec 182 MBytes 152 Mbits/sec [ 3] 130.0-140.0 sec 182 MBytes 152 Mbits/sec [ 3] 140.0-150.0 sec 181 MBytes 152 Mbits/sec [ 3] 150.0-160.0 sec 181 MBytes 152 Mbits/sec [ 3] 160.0-170.0 sec 180 MBytes 151 Mbits/sec [ 3] 170.0-180.0 sec 180 MBytes 151 Mbits/sec [ 3] 180.0-190.0 sec 180 MBytes 151 Mbits/sec [ 3] 190.0-200.0 sec 180 MBytes 151 Mbits/sec [ 3] 200.0-210.0 sec 180 MBytes 151 Mbits/sec [ 3] 210.0-220.0 sec 181 MBytes 152 Mbits/sec [ 3] 220.0-230.0 sec 180 MBytes 151 Mbits/sec [ 3] 230.0-240.0 sec 181 MBytes 152 Mbits/sec [ 3] 240.0-250.0 sec 181 MBytes 152 Mbits/sec [ 3] 250.0-260.0 sec 181 MBytes 152 Mbits/sec [ 3] 260.0-270.0 sec 180 MBytes 151 Mbits/sec [ 3] 270.0-280.0 sec 181 MBytes 152 Mbits/sec [ 3] 280.0-290.0 sec 180 MBytes 151 Mbits/sec [ 3] 290.0-300.0 sec 180 MBytes 151 Mbits/sec [ 3] 0.0-300.0 sec 5.32 GBytes 152 Mbits/sec pi@raspberrypi:~ $
The transfer rate from the Pi to the Mac over the usb interface is on average 152 MBit/s.
The other direction for a data transfer from the Mac to the Pi shows a data rate of 109 MBit/s. For that test I started the iperf server on the Pi and called the iperf client on the Mac.
Fredo:~ fritz$ iperf -i 10 -t 100 -c 192.168.2.2 ------------------------------------------------------------ Client connecting to 192.168.2.2, TCP port 5001 TCP window size: 129 KByte (default) ------------------------------------------------------------ [ 4] local 192.168.2.1 port 63206 connected with 192.168.2.2 port 5001 [ ID] Interval Transfer Bandwidth [ 4] 0.0-10.0 sec 130 MBytes 109 Mbits/sec [ 4] 10.0-20.0 sec 130 MBytes 109 Mbits/sec [ 4] 20.0-30.0 sec 130 MBytes 109 Mbits/sec [ 4] 30.0-40.0 sec 130 MBytes 109 Mbits/sec [ 4] 40.0-50.0 sec 130 MBytes 109 Mbits/sec [ 4] 50.0-60.0 sec 130 MBytes 109 Mbits/sec [ 4] 60.0-70.0 sec 130 MBytes 109 Mbits/sec [ 4] 70.0-80.0 sec 130 MBytes 109 Mbits/sec [ 4] 80.0-90.0 sec 130 MBytes 109 Mbits/sec [ 4] 90.0-100.0 sec 130 MBytes 109 Mbits/sec [ 4] 0.0-100.0 sec 1.27 GBytes 109 Mbits/sec Fredo:~ fritz$
The transfer rate from the Mac to the Pi is 109 Mbit/s over the USB Interface.
CPU Load during iperf transfer
I measured the cpu load with the top tool. I login to the pi via the wifi interface and run “top” there. The idle sitation is shown here:
top - 13:29:01 up 33 min, 2 users, load average: 0.03, 0.04, 0.00
Tasks: 77 total, 1 running, 76 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.7 us, 1.0 sy, 0.0 ni, 98.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
MiB Mem : 432.7 total, 327.0 free, 36.6 used, 69.1 buff/cache
MiB Swap: 100.0 total, 100.0 free, 0.0 used. 345.0 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
578 pi 20 0 10172 2952 2520 R 1.0 0.7 0:01.11 top
556 root 20 0 0 0 0 I 0.3 0.0 0:00.02 kworker/u+
1 root 20 0 32532 7876 6384 S 0.0 1.8 0:04.33 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
5 root 20 0 0 0 0 I 0.0 0.0 0:00.04 kworker/u+
6 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mm_percpu+
7 root 20 0 0 0 0 S 0.0 0.0 0:00.31 ksoftirqd+
8 root 20 0 0 0 0 S 0.0 0.0 0:00.01 kdevtmpfs
9 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 netns
10 root 20 0 0 0 0 I 0.0 0.0 0:00.10 kworker/0+
11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd
Then I start the iperf client and transfer the data to the iperf server on the Mac. The cpu load on the Pi looks like this:
top - 13:30:54 up 35 min, 2 users, load average: 0.61, 0.17, 0.05
Tasks: 77 total, 2 running, 75 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.7 us, 46.7 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 52.6 si, 0.0 st
MiB Mem : 432.7 total, 326.0 free, 37.5 used, 69.2 buff/cache
MiB Swap: 100.0 total, 100.0 free, 0.0 used. 344.0 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
580 pi 20 0 26708 2944 2252 S 80.7 0.7 0:20.34 iperf
7 root 20 0 0 0 0 R 14.1 0.0 0:03.64 ksoftirqd+
299 root 20 0 27640 1368 1240 S 3.6 0.3 0:01.11 rngd
578 pi 20 0 10172 2952 2520 R 0.7 0.7 0:01.97 top
91 root 20 0 0 0 0 I 0.3 0.0 0:00.51 kworker/u+
562 pi 20 0 12172 4056 3248 S 0.3 0.9 0:00.37 sshd
579 root 20 0 0 0 0 I 0.3 0.0 0:00.18 kworker/0+
1 root 20 0 32532 7876 6384 S 0.0 1.8 0:04.33 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
5 root 20 0 0 0 0 I 0.0 0.0 0:00.04 kworker/u+
6 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mm_percpu+
The CPU is fully loaded with the iperf process (80%) and the interrupt service (14%). The transfer rate is again 150 MBit/s.
ssh transfer via usb
I created 3 files with different size
- tf1mb - 1 MB
- tf3mb - 3 MB
- tf100mb - 100Mb
The following example creates the file “tf3mb” with random content and a size of 3000000 bytes (3 MB).
pi@raspberrypi:~ $ dd if=/dev/urandom of=tf3mb bs=1000 count=3000 3000+0 records in 3000+0 records out 3000000 bytes (3.0 MB, 2.9 MiB) copied, 0.272827 s, 11.0 MB/s pi@raspberrypi:
The I copied the file from the Pi to the Mac via scp.
Fredo:~ fritz$ scp pi@192.168.2.2:~/tf1mb . pi@192.168.2.2's password: tf1mb 100% 977KB 4.8MB/s 00:00 Fredo:~ fritz$ scp pi@192.168.2.2:~/tf3mb . pi@192.168.2.2's password: tf3mb 100% 2930KB 5.1MB/s 00:00 Fredo:~ fritz$ scp pi@192.168.2.2:~/tf100mb . pi@192.168.2.2's password: tf100mb 100% 95MB 5.2MB/s 00:18 Fredo:~ fritz$
The reported rate is 5.2 MB/s. The transfer time as reported by scp -v is shown in the following table together with the effective rate.
| File | Size | Time | Rate |
|---|---|---|---|
| tf1mb | 1000000 Bytes | 0.6 s | 13 MBit/s |
| tf3mb | 3000000 Bytes | 0.9 s | 27 MBit/s |
| tf100mb | 100000000 Bytes | 18.8 s | 42 MBit/s |
The transfer rate depends on the file size. Compared to the rate of 150 MBit/s as reported by iperf, there is substantial mismatch. The CPU load during the transfer as shown by top is
top - 14:55:32 up 2:00, 3 users, load average: 0.52, 0.15, 0.13
Tasks: 82 total, 3 running, 79 sleeping, 0 stopped, 0 zombie
%Cpu(s): 53.3 us, 35.9 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 10.8 si, 0.0 st
MiB Mem : 432.7 total, 217.3 free, 41.1 used, 174.3 buff/cache
MiB Swap: 100.0 total, 100.0 free, 0.0 used. 339.5 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
948 pi 20 0 12320 4244 3320 R 89.2 1.0 0:13.13 sshd
950 pi 20 0 6648 1828 1724 S 7.5 0.4 0:01.12 scp
299 root 20 0 27640 1380 1240 S 1.3 0.3 0:19.77 rngd
7 root 20 0 0 0 0 R 1.0 0.0 2:32.59 ksoftirqd/0
918 pi 20 0 10168 2848 2428 R 1.0 0.6 0:00.71 top
43 root -51 0 0 0 0 S 0.3 0.0 1:25.49 irq/86-mmc1
1 root 20 0 32532 7884 6384 S 0.0 1.8 0:05.07 systemd
The CPU is fully loaded. 90% of the time is spent in the ssh daemon. This is probably due to the encryption of ssh. The rate is limited by CPU load. For short files the initial transactions probably limit the rate.
http transfer via USB
I installed the lighttpd web server on the Raspberry Pi and tested the file transfer via wget.
Fredo:~ fritz$ wget 192.168.2.2/tf100mb --2019-11-27 16:52:57-- http://192.168.2.2/tf100mb Verbindungsaufbau zu 192.168.2.2:80 … verbunden. HTTP-Anforderung gesendet, auf Antwort wird gewartet … 200 OK Länge: 100000000 (95M) [application/octet-stream] Wird in »tf100mb.2« gespeichert. tf100mb.2 100%[========================================================>] 95,37M 18,6MB/s in 5,2s 2019-11-27 16:53:02 (18,5 MB/s) - »tf100mb.2« gespeichert [100000000/100000000] Fredo:~ fritz$
It takes 5.2s to transfer the 100MB file. That corresponds to a speed of 153 Mbit/s. The full usb speed according to iperf is used. The transfer times for the 1MB file are 0.06s and for the 3MB file 0.2s.
iperf measurements via WLAN
In my setup the Pi and Macbook both connect to a Fritzbox and both receive their IP address via DHCP. The IP address of the Pi is 192.168.178.84 and the IP Address of the Macbook is 192.168.178.34. The iperf server is started on the Macbook and the client on the Pi. The FritzBox access point is operates on 2.4 GHz channel 1. The fritzbox reports 8 others stations on that band. The distance between the Fritzbox and the Pi is approximately 2m. The Fritzbox reports that the wifi rate of the Pi is 65 Mbit/s for upstream and downstream.
pi@raspberrypi:~ $ iperf -i 10 -t 300 -c 192.168.178.34 ------------------------------------------------------------ Client connecting to 192.168.178.34, TCP port 5001 TCP window size: 74.4 KByte (default) ------------------------------------------------------------ [ 3] local 192.168.178.84 port 53842 connected with 192.168.178.34 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 46.9 MBytes 39.3 Mbits/sec [ 3] 10.0-20.0 sec 48.9 MBytes 41.0 Mbits/sec [ 3] 20.0-30.0 sec 49.2 MBytes 41.3 Mbits/sec [ 3] 30.0-40.0 sec 47.1 MBytes 39.5 Mbits/sec [ 3] 40.0-50.0 sec 45.6 MBytes 38.3 Mbits/sec [ 3] 50.0-60.0 sec 48.5 MBytes 40.7 Mbits/sec [ 3] 60.0-70.0 sec 48.9 MBytes 41.0 Mbits/sec [ 3] 70.0-80.0 sec 48.8 MBytes 40.9 Mbits/sec [ 3] 80.0-90.0 sec 48.5 MBytes 40.7 Mbits/sec [ 3] 90.0-100.0 sec 48.2 MBytes 40.5 Mbits/sec [ 3] 100.0-110.0 sec 48.6 MBytes 40.8 Mbits/sec [ 3] 110.0-120.0 sec 47.2 MBytes 39.6 Mbits/sec [ 3] 120.0-130.0 sec 48.5 MBytes 40.7 Mbits/sec [ 3] 130.0-140.0 sec 48.2 MBytes 40.5 Mbits/sec [ 3] 140.0-150.0 sec 47.9 MBytes 40.2 Mbits/sec [ 3] 150.0-160.0 sec 47.9 MBytes 40.2 Mbits/sec [ 3] 160.0-170.0 sec 49.6 MBytes 41.6 Mbits/sec [ 3] 170.0-180.0 sec 47.0 MBytes 39.4 Mbits/sec [ 3] 180.0-190.0 sec 45.4 MBytes 38.1 Mbits/sec [ 3] 190.0-200.0 sec 44.5 MBytes 37.3 Mbits/sec [ 3] 200.0-210.0 sec 47.1 MBytes 39.5 Mbits/sec [ 3] 210.0-220.0 sec 44.0 MBytes 36.9 Mbits/sec [ 3] 220.0-230.0 sec 45.5 MBytes 38.2 Mbits/sec [ 3] 230.0-240.0 sec 48.4 MBytes 40.6 Mbits/sec [ 3] 240.0-250.0 sec 48.5 MBytes 40.7 Mbits/sec [ 3] 250.0-260.0 sec 48.6 MBytes 40.8 Mbits/sec [ 3] 260.0-270.0 sec 48.4 MBytes 40.6 Mbits/sec [ 3] 270.0-280.0 sec 48.0 MBytes 40.3 Mbits/sec [ 3] 280.0-290.0 sec 46.5 MBytes 39.0 Mbits/sec [ 3] 290.0-300.0 sec 47.5 MBytes 39.8 Mbits/sec [ 3] 0.0-300.0 sec 1.39 GBytes 39.9 Mbits/sec pi@raspberrypi:~ $
The average data rate from the Pi to the Mac via 2.4 GHz Wifi measured with iperf is 39.9 MBit/s.
CPU load during iperf wlan transfer
top results during iperf data transfer
top - 13:59:35 up 1:04, 3 users, load average: 1.29, 0.92, 0.53
Tasks: 80 total, 1 running, 79 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.7 us, 22.2 sy, 0.0 ni, 44.7 id, 0.0 wa, 0.0 hi, 32.4 si, 0.0 st
MiB Mem : 432.7 total, 321.6 free, 41.0 used, 70.1 buff/cache
MiB Swap: 100.0 total, 100.0 free, 0.0 used. 340.5 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
556 root 20 0 0 0 0 I 24.9 0.0 0:27.56 kworker/u2:1-brcmf_wq/mmc1:0001:1
7 root 20 0 0 0 0 S 14.2 0.0 1:33.28 ksoftirqd/0
43 root -51 0 0 0 0 S 11.7 0.0 0:34.95 irq/86-mmc1
662 pi 20 0 26708 3116 2052 S 2.3 0.7 0:04.38 iperf
665 pi 20 0 10168 3004 2584 R 1.3 0.7 0:00.57 top
657 root 20 0 0 0 0 I 0.6 0.0 0:48.06 kworker/u2:0-brcmf_wq/mmc1:0001:1
299 root 20 0 27640 1380 1240 S 0.3 0.3 0:17.01 rngd
533 pi 20 0 12172 4016 3208 S 0.3 0.9 0:00.22 sshd
1 root 20 0 32532 7876 6384 S 0.0 1.8 0:04.41 systemd
The iperf client transfer results in a CPU load of 50%. The iperf process consumes only 3%, while most of the cpu power goes to the interrupt handling of the wlan driver.
ssh transfer with wlan
The ssh results for the wifi transfer are
Fredo:~ fritz$ scp pi@192.168.178.84:~/tf1mb . pi@192.168.178.84's password: tf1mb 100% 977KB 2.1MB/s 00:00 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf3mb . pi@192.168.178.84's password: tf3mb 100% 2930KB 2.3MB/s 00:01 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf100mb . pi@192.168.178.84's password: tf100mb 100% 95MB 1.6MB/s 00:58 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf100mb . pi@192.168.178.84's password: tf100mb 100% 95MB 1.8MB/s 00:54 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf100mb . pi@192.168.178.84's password: tf100mb 100% 95MB 1.8MB/s 00:53 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf100mb . pi@192.168.178.84's password: tf100mb 100% 95MB 1.7MB/s 00:55 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf100mb . pi@192.168.178.84's password: tf100mb 100% 95MB 1.9MB/s 00:51 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf1mb . pi@192.168.178.84's password: tf1mb 100% 977KB 1.8MB/s 00:00 Fredo:~ fritz$ scp pi@192.168.178.84:~/tf3mb . pi@192.168.178.84's password: Permission denied, please try again. pi@192.168.178.84's password: tf3mb 100% 2930KB 2.0MB/s 00:01 Fredo:~ fritz$
During the transfer of the 100 MByte file, the cpu load according to top is
top - 15:36:21 up 18 min, 1 user, load average: 0.96, 0.86, 0.58
Tasks: 76 total, 2 running, 74 sleeping, 0 stopped, 0 zombie
%Cpu(s): 23.3 us, 39.5 sy, 0.0 ni, 3.9 id, 0.0 wa, 0.0 hi, 33.3 si, 0.0 st
MiB Mem : 432.7 total, 222.8 free, 40.1 used, 169.7 buff/cache
MiB Swap: 100.0 total, 100.0 free, 0.0 used. 341.3 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
906 pi 20 0 15852 7740 3208 R 29.5 1.7 0:08.32 sshd
314 root 20 0 0 0 0 D 29.2 0.0 0:50.23 kworker/u2:3++
43 root -51 0 0 0 0 D 28.8 0.0 1:20.66 irq/86-mmc1
908 pi 20 0 6620 1760 1656 S 3.2 0.4 0:00.70 scp
7 root 20 0 0 0 0 S 2.6 0.0 0:12.60 ksoftirqd/0
530 pi 20 0 10172 2856 2432 R 1.0 0.6 0:08.43 top
292 root 20 0 27640 1420 1292 S 0.6 0.3 0:01.62 rngd
The CPU is fully loaded and 30% are used for the ssh daemon and 60% are required for the wifi driver. It takes about 55s to transfer the 100 MB file. The rate is therefore around 14 MBit/s. The 1MB files take 0.8s (=10 MBit/s) and the 3MB file takes 2.5s (=10 MBit/s).
http transfer time for wifi
The results for the wget transfer time are 0.8s for the 1MB file, 1.1s for the 3MB file and 30s for teh 100MB file. However, these measurements were made at 19.00, i.e. there is quite some traffic on channel 1 now…
The transfer times for the 100MB were 30s, 24s, 25s, 26s. This corresponds to a transfer rate of 30 MBit/s. Some times for the 1MB file were: 0.2 0.2 0.2 0.9 0.3 0.7 0.7 0.2 → There is heavy congestion on channel 1.
Based on the 0.2s for the 1 MB File, this translates to 5 MB/s = 40 MBit/s rate for an undisturbed channel for a transfer via http. This is again exactly the achieved iperf rate as shown above.
Julian tests
- WIFI Only datatransfer
- Router: FritzBox 7430 AW
- Placement: Pi Zero and Laptop placed 10cm above router.
- data ammount: 540 MByte
- Laptop and Raspberry Pi share the same Wifi channel ⇒ Each packet goes from Pi to AP and from AP to Laptop. ⇒ Congestion on the Wifi Channel.
wget
- time=213sek
- rate=2.53 Mbyte/sek
- cpuusage=70%
ftp
- time=361sek
- rate=1.495 Mbyte/sek
- cpuusage=50-60%
Results
- The Laptop and the Pi should not be connected via a single 2.4 GHz access point as laptop and Pi share the same Wifi channel. This results in 50% throughput reduction (see Julians 2.5 MB/s for wget).
- The transfer rate via wget on an undisturbed 2.4 GHz wifi channel is 5 MB/s. (Only Pi connected to AP, No other stations use this channel). This 40 MBit/s throughput on http level compares well to the maximum 65 MBit/s wifi data rate of the Pi Zero W.
- ssh transfer is limited by CPU load on the Pi for encryption and results in 1.8 MB/s for Wifi.
- Short Guard Interval setting could possibly increase the the raw wifi rate from 65 MBit/s to 72 MBit/s.
Pi4/CM4 data transfer rate test
- Fritzbox 7520
- CM4 5Ghz Wifi
- Laptop T14 via Gigabit Ethernet
pi4 theoretical speed
from https://forums.raspberrypi.com/viewtopic.php?t=291824&start=25#p1768600
Fri Nov 27, 2020 2:03 pm The WiFi chip is connected via a 4-bit SDIO link that typically runs at 41.7MHz giving an upper limit on throughput of ~160Mbs. In practise you won't get close to that because it is a simplex link (only one direction at a time) and there is overhead in each of the protocol and transport layers. Given that, 112Mbps sounds pretty good. Even though the throughput hasn't increased, being able to properly use the wide channels means that the channel (which is a shared medium) is occupied for a shorter time, leaving more time for other devices.
pi4 config
pi@testi:~ $ iw dev
phy#0
Unnamed/non-netdev interface
wdev 0x2
addr de:a6:32:fe:85:b0
type P2P-device
txpower 31.00 dBm
Interface wlan0
ifindex 3
wdev 0x1
addr dc:a6:32:fe:85:b0
ssid DrMartinRouterKing
type managed
channel 64 (5320 MHz), width: 80 MHz, center1: 5290 MHz
txpower 31.00 dBm
pi@testi:~ $ iwconfig wlan0
wlan0 IEEE 802.11 ESSID:"XXXXXXXXXXXX"
Mode:Managed Frequency:5.32 GHz Access Point: 3C:A6:2F:CB:E0:7E
Bit Rate=433.3 Mb/s Tx-Power=31 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:on
Link Quality=70/70 Signal level=-29 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:1 Invalid misc:0 Missed beacon:0
iperf measurements via WLAN
Datatransfer Pi4 -> Laptop
➜ /tmp iperf3 -s ----------------------------------------------------------- Server listening on 5201 (test #1) ----------------------------------------------------------- Accepted connection from 192.168.178.29, port 54534 [ 5] local 192.168.178.20 port 5201 connected to 192.168.178.29 port 54536 [ ID] Interval Transfer Bitrate [ 5] 0.00-1.00 sec 9.14 MBytes 76.7 Mbits/sec [ 5] 1.00-2.00 sec 10.8 MBytes 90.9 Mbits/sec [ 5] 2.00-3.00 sec 10.9 MBytes 91.1 Mbits/sec [ 5] 3.00-4.00 sec 10.8 MBytes 90.9 Mbits/sec [ 5] 4.00-5.00 sec 10.9 MBytes 91.5 Mbits/sec [ 5] 5.00-6.00 sec 10.3 MBytes 86.2 Mbits/sec [ 5] 6.00-7.00 sec 9.21 MBytes 77.3 Mbits/sec [ 5] 7.00-8.00 sec 10.9 MBytes 91.1 Mbits/sec [ 5] 8.00-9.00 sec 10.8 MBytes 90.7 Mbits/sec [ 5] 9.00-10.00 sec 10.9 MBytes 91.5 Mbits/sec [ 5] 10.00-10.01 sec 103 KBytes 89.2 Mbits/sec - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bitrate [ 5] 0.00-10.01 sec 105 MBytes 87.8 Mbits/sec receiver ----------------------------------------------------------- Server listening on 5201 (test #2) ----------------------------------------------------------- ^Ciperf3: interrupt - the server has terminated
Datatransfer Pi4 <- Laptop
➜ /tmp iperf3 -c 192.168.178.29 iperf3: error - unable to connect to server: Connection refused ➜ /tmp iperf3 -c 192.168.178.29 Connecting to host 192.168.178.29, port 5201 [ 5] local 192.168.178.20 port 40318 connected to 192.168.178.29 port 5201 [ ID] Interval Transfer Bitrate Retr Cwnd [ 5] 0.00-1.00 sec 5.21 MBytes 43.7 Mbits/sec 24 24.0 KBytes [ 5] 1.00-2.00 sec 4.57 MBytes 38.4 Mbits/sec 32 22.6 KBytes [ 5] 2.00-3.00 sec 4.75 MBytes 39.8 Mbits/sec 35 38.2 KBytes [ 5] 3.00-4.00 sec 5.11 MBytes 42.8 Mbits/sec 36 28.3 KBytes [ 5] 4.00-5.00 sec 4.51 MBytes 37.9 Mbits/sec 24 31.1 KBytes [ 5] 5.00-6.00 sec 5.11 MBytes 42.8 Mbits/sec 31 21.2 KBytes [ 5] 6.00-7.00 sec 5.23 MBytes 43.8 Mbits/sec 23 35.4 KBytes [ 5] 7.00-8.00 sec 5.46 MBytes 45.8 Mbits/sec 27 21.2 KBytes [ 5] 8.00-9.00 sec 4.99 MBytes 41.8 Mbits/sec 20 35.4 KBytes [ 5] 9.00-10.00 sec 4.63 MBytes 38.9 Mbits/sec 41 19.8 KBytes - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bitrate Retr [ 5] 0.00-10.00 sec 49.6 MBytes 41.6 Mbits/sec 293 sender [ 5] 0.00-10.00 sec 49.3 MBytes 41.4 Mbits/sec receiver iperf Done.