WiFi very slow to connect on boot-up

This is a know bug/feature in Linux. The solution:

Found a solution, it seems that the new kernels are compiled with "Accelerate last non-dyntick-idle CPU's grace periods (RCU_FAST_NO_HZ)" option: Yes

explanation from the Linux kernel source:

This option causes RCU to attempt to accelerate grace periods
in order to allow CPUs to enter dynticks-idle state more
quickly. On the other hand, this option increases the overhead
of the dynticks-idle checking, particularly on systems with
large numbers of CPUs.

If you add

nohz=off

to the kernel line in grub the "NOHZ local_softirq_pending"  messages don't show up

This is a know bug/feature in Linux. The solution:

Found a solution, it seems that the new kernels are compiled with "Accelerate last non-dyntick-idle CPU's grace periods (RCU_FAST_NO_HZ)" option: Yes

explanation from the Linux kernel source:

This option causes RCU to attempt to accelerate grace periods
in order to allow CPUs to enter dynticks-idle state more
quickly. On the other hand, this option increases the overhead
of the dynticks-idle checking, particularly on systems with
large numbers of CPUs.

If you add

nohz=off

to the kernel line in grub the "NOHZ local_softirq_pending"  messages don't show up

A better wording:

Add nohz=off to the kernel parameters during boot to disable it.

This option causes RCU to attempt to accelerate grace periods in order to allow CPUs to enter dynticks-idle state more quickly. On the other hand, this option increases the overhead of the dynticks-idle checking, particularly on systems with large numbers of CPUs.

But this really a symptom of DHCP from the router being slow!

Hello,

Thanks for your response but those messages have nothing to do with the wifi problem and are not cause any issue, they were just on the console when I cut-n-pasted the wifi driver logs.    Also DHCP is not involved here, notice that I said I set my system up with a static IP on my "private" network so I don't have to deal with dynamic IPs.

jeff

Sorry missed that static word.

Hi Jeff,

When you say it takes a long time for the network to come up what does that mean?

How are nameservers getting assigned if you use a static IP address since those are normally assigned by the DHCP server?

Are you sure that it is not something else networking related?

https://www.linuxquestions.org/questions/linux-networking-3/network-very-slow-if-static-ip-settings-but-fine-with-dhcp-7…

Do you see the same issue when using a static IP address with a USB-Ethernet adapter on Ultra96?

Best Regards,

-Kevin

Hello,

By slow, it means I can see the system boot on the console and after that I try to access the system, either by ping or ssh.  5 seconds is probably generous, typically it's longer(if at all)

Here is my setup

     - Vonets Var11N-300 to create a hotspot

     - USB wifi dongle plugged into my Ubunutu deskside

     - static IP assigned in /etc/network/interfaces

This is just a "private" network to give a direct connection from my deskside to the ultra96 so no external network access.

I just tried going back to dhcp and this takes a while to get a IP address but I was unable to ping or login.  If I run /etc/init.d/network restart I can then get access.  I see the same thing with a static IP.  If I can't ssh in, I restart the network and it immediately works.

Perhaps, the wilc driver is being loaded to late?  How does the system know which wifi driver to load?  I don't see anything obvious and I wonder if it could be loaded earlier?

Also, I don't have a adaptor.  Can you tell me the name of a USB-ethernet adapter that works.

thanks,

jeff

I have used this one successfully -- https://www.newark.com/prudent-way/pwi-usb-lan/usb-2-0-to-ethernet-adapter-driverless/dp/88W0412

Bryan

Hi Jeff,

What machine are you pinging Ultra96 from?  Is it the Ubuntu Desktop?  If so, is the ARP cache getting cleared under Ubuntu during the Ultra96 reboot?  If so, then Ubuntu will have to resolve the IP address you are pinging down to the Ultra96 MAC which can take some time for ARP tables of the router to update if they are also getting cleared when Ultra96 WiFi goes down.

To make your network setup more deterministic and still get a known IP assignment, could you go the other way around?

On your Vonets Var11N-300 do you have the ability to make a static entry for your Ultra96 in the DHCP assignment table?  Some more advanced routers can do this so that you can still use DHCP on your machines but they get assigned specific IP addresses based upon the MAC that is reported to the DHCP server during the IP lease request. 

I use pfSense on my network and so I can assign an IP address outside the dynamically assigned range to a specific MAC address (like my Ultra96 board, ZedBoard, UltraZed boards, etc.) so that when they do a DHCP they get a known fixed IP address assigned by my DHCP server plus the gateway and nameservers get setup correctly as well

Static DHCP Mapping in pfSense - pfSense Setup HQ

Best Regards,

-Kevin