rahlquist
Posts: 146
Joined: Tue Jan 21, 2014 1:02 pm

Wifi horribly slow. RTL8188CUS

Thu Jan 23, 2014 3:20 pm

Hello,

For Christmas I was given a Pi in a kit http://goo.gl/vJOm7x I have been tinkering ever since. One issue I have is wifi speed. It is beyond slow and with the Pi it seems as the network works harder or gets more backed up the cpu use slowly climbs. Using iperf to test speed to one of my machines I get 505 Kbits/sec to 2.9 Mbits/sec. From a laptop, on the same network and frequency in the same location I get 25.8 Mbits/sec. Any suggestions as to what I can do to fix this issue? Here is some info about my setup.

Code: Select all

pi@rb1 ~ $ uname -a
Linux rb1 3.10.26+ #628 PREEMPT Fri Jan 10 17:18:51 GMT 2014 armv6l GNU/Linux

pi@rb1 ~ $ lsusb
Bus 001 Device 004: ID 0bda:8176 Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter

pi@rb1 ~ $ modinfo 8192cu
filename:       /lib/modules/3.10.26+/kernel/drivers/net/wireless/rtl8192cu/8192cu.ko
version:        v4.0.2_9000.20130911

pi@rb1 ~ $ sudo ifconfig
eth0      Link encap:Ethernet  HWaddr b8:27:eb:73:6d:8b
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

wlan0     Link encap:Ethernet  HWaddr 00:13:ef:90:02:94
          inet addr:192.168.0.93  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:31899 errors:0 dropped:64216 overruns:0 frame:0
          TX packets:35466 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:4325604 (4.1 MiB)  TX bytes:48729692 (46.4 MiB)

pi@rb1 ~ $ sudo iwconfig
wlan0     IEEE 802.11bgn  ESSID:"AREN2109"  Nickname:"<WIFI@REALTEK>"
          Mode:Managed  Frequency:2.462 GHz  Access Point: C0:C1:C0:0A:7E:3D
          Bit Rate:72.2 Mb/s   Sensitivity:0/0
          Retry:off   RTS thr:off   Fragment thr:off
          Encryption key:****-****-****-****-****-****-****-****   Security mode:open
          Power Management:off
          Link Quality=100/100  Signal level=100/100  Noise level=0/100
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

lo        no wireless extensions.

eth0      no wireless extensions.

pi@rb1 ~ $ cat /etc/network/interfaces

auto lo

iface lo inet loopback
iface eth0 inet dhcp

auto wlan0
allow-hotplug wlan0
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp
wireless-power off

pi@rb1 ~ $ cat  /etc/wpa_supplicant/wpa_supplicant.conf
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
        ssid="AREN2109"
        psk="<mykey>"
        proto=RSN
        key_mgmt=WPA-PSK
        pairwise=CCMP
        group=CCMP
        auth_alg=OPEN
        priority=9
}

User avatar
DougieLawson
Posts: 29329
Joined: Sun Jun 16, 2013 11:19 pm
Location: Basingstoke, UK
Contact: Website

Re: Wifi horribly slow. RTL8188CUS

Thu Jan 23, 2014 9:45 pm

Try this:

Code: Select all

sudo -i
echo "options 8192cu rtw_power_mgnt=0 rtw_enusbss=0" > /etc/modprobe.d/8192cu.conf 
exit
Then reboot.
Microprocessor, Raspberry Pi & Arduino Hacker
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Please post ALL technical questions on the forum. Do not send private messages.

rahlquist
Posts: 146
Joined: Tue Jan 21, 2014 1:02 pm

Re: Wifi horribly slow. RTL8188CUS

Thu Jan 23, 2014 11:58 pm

DougieLawson wrote:Try this:

Code: Select all

sudo -i
echo "options 8192cu rtw_power_mgnt=0 rtw_enusbss=0" > /etc/modprobe.d/8192cu.conf 
exit
Then reboot.
No change after reboot. Dumped the remaining settings related to this

https://www.dropbox.com/s/zykc2g8ai4kyx5e/settings.log

rahlquist
Posts: 146
Joined: Tue Jan 21, 2014 1:02 pm

Re: Wifi horribly slow. RTL8188CUS

Fri Jan 24, 2014 7:40 pm

So I took another track. A friend has been using the Edimax Technology Co., Ltd EW-7811Un and having no issues. So I bought one. It arrived today, powered down Pi, took out old wifi, plugged in new and bam 42 Mbit/sec.

New
Bus 001 Device 004: ID 7392:7811 Edimax Technology Co., Ltd EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS]
old
Bus 001 Device 004: ID 0bda:8176 Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter

Ok so same tech, same module and I didnt change a flipping setting and there is this much difference?

I compared all the settings for the module and they all report back the same. All I can guess at this point is the first adapter is bad? I will try it in a windows machine tonight and see how it works.

rahlquist
Posts: 146
Joined: Tue Jan 21, 2014 1:02 pm

Re: Wifi horribly slow. RTL8188CUS

Sat Jan 25, 2014 12:06 am

Ok I think I worked out the problem with the old one, or at least figured it out. Doubt I will be able to do anything about making it work better. The adapter is VERY voltage sensitive. I have a inline USB power meter that measure current use, in the process of doing this it introduces a small (.2-.5v) drop in voltage. If I put this adapter directly into USB port of my old laptop it will give me up to 19Mb/sec. If I put the power meter inline it drops to 9M/sec. If I put an unpowered hub on the latop, then the power meter, then a adjustable usb gooseneck I get 7.58Mb/sec. If I add a usb extension cord to that mix I get 6.05M/sec. So with each voltage drop the speed goes down. According to the power meter the dongle is drawing less than 1watt, though it gets hot, 47-50deg C according to my spot thermometer and thats just with a 30 second burst of iperf running. Also if I change the hookup order to Laptop to powermeter to extension to hub to gooseneck I get the powermeter showing 2 watts used when under load.

So it seems this adapter which by all appearances is the same model as adafruit sells is very voltage sensitive. I dont have a bench supply and a powered usb hub to verify this with but the fact that the more load I put between the adapter and the USB port least me to believe this is the right answer. If there is anything anyone else can think of to try let me know. If you have the facilities/tools to properly test or verify my findings I will be happy to drop this adapter in the mail.

jonnyboy
Posts: 1
Joined: Sat Jul 26, 2014 5:28 am

Re: Wifi horribly slow. RTL8188CUS

Sat Jul 26, 2014 5:47 am

rahlquist wrote:So I took another track. A friend has been using the Edimax Technology Co., Ltd EW-7811Un and having no issues. So I bought one. It arrived today, powered down Pi, took out old wifi, plugged in new and bam 42 Mbit/sec.

New
Bus 001 Device 004: ID 7392:7811 Edimax Technology Co., Ltd EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS]
old
Bus 001 Device 004: ID 0bda:8176 Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter

Ok so same tech, same module and I didnt change a flipping setting and there is this much difference?

I compared all the settings for the module and they all report back the same. All I can guess at this point is the first adapter is bad? I will try it in a windows machine tonight and see how it works.

I hate to bump this post (it's not too too old), but is your Edimax EW-7811Un still working much better? My adapter (your old one, shows up exactly the same in lsusb ID 0bda:8176) seemed to get much worse pretty quickly. I'm assuming this is what you're talking about in terms of replacement: http://www.amazon.com/Edimax-EW-7811Un- ... +ew-7811un

Just want to make sure I get it right this time...so is there anything you suggest?
Also, you configured your Pi for the first adapter and then the second one worked out of the box with the same config correct?
Thank you!

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