CPU (core) maxed and seeing wifi disconnects

[fr33z0n3r]

In the past few months I've been dealing with an odd wifi disconnect issue. I am now suspecting an issue with my AC68U router running Merlin 378.56_2. I tend to be on 5ghz, but also have 2.4 setup.

I just experienced the drop from my phone - where I always notice it, but I also had my tablet say the network dropped. Because I saw both at the same time, I thought it was odd and checked the router.

On the CPU chart, one of the 2 cores was maxed at 100%. And so I ssh'd in to see if I could identify a process, but all it shows was io was ~50%. I don't know what this means or if this was a known bug.

I guess io indicates disk activity. And there is no iotop to dig into usage. Would anything be in the syslog by default about possible activity? Any other way to troubleshoot this?

I could not get it to reboot from the web gui. I unplugged it and that stopped the issue.

My web mgmt port only https on port 443. I also use ipv6 tunnel and a openvpn server.

Any ideas?

 

[Hawk]

Just guessing but it might be possible cpu is overloaded and is not able to process wifi traffic. I read about wifi processing done on main cpu in rt-ac68u. It could very well be one which max to 100 percent.
Try disabling 1pv6 tunnel and see if it helps.

 

[RMerlin]

You I/O reports 49% using CPU (in a dual core setup this means one core at 100%). Do you have any USB disk plugged in?

Also check dmesg or /tmp/syslog.log for any error message.

 

[Sunny]

Had similar issue with my RT-AC68R where my whole home network would come to a crawl every few days apart, using the top command there were no processes to blame just some io and sirq

I updated to the latest 378.58 and its only happened once since (touch wood)

I have a 32gb usb stick plugged in shared via NFS for storing some ESXI VM settings, but I believe its just a few kb of data and minimal usage.

 

[zahroc]

I have had the same issue on a RT-AC87R. I have not done any investigation but each of the two times I just powered it down and rebooted.

 

[john9527]

You I/O reports 49% using CPU (in a dual core setup this means one core at 100%). Do you have any USB disk plugged in?

Also check dmesg or /tmp/syslog.log for any error message.

Just as an FYI....after starting top, it you press '1' it will show the stats for each CPU individually....

 

[RMerlin]

Just as an FYI....after starting top, it you press '1' it will show the stats for each CPU individually....

Cool. Busybox applets are usually so cut-down, I never really bother trying to find out what advanced features they support (or don't)

BB netstat's lack of support for identifying which process is listening to a socket is what makes me keep a copy of the full-featured netstat tool around.

 

[sfx2000]

Cool. Busybox applets are usually so cut-down, I never really bother trying to find out what advanced features they support (or don't)

They're actually not applets in Busybox, they're functions within a single binary - if one looks at the file system, you'll see that most commands in a Busybox system are symbolic/soft links to busybox...

Busybox is cool... between it, uClibc, and Dropbear... the kernel lives in the small footprint that most consumer AP/Routers exist in...

Again however, it's that small footprint that holds folks back - even with a $500USD Router/AP that has 512MB RAM and 128MB flash... and that's pretty sad.

But at least it looks cool...

 

[RMerlin]

They're actually not applets in Busybox, they're functions within a single binary - if one looks at the file system, you'll see that most commands in a Busybox system are symbolic/soft links to busybox...

You probably don't have the same definition of applets as I do. The fact that Busybox can be compiled as a bunch of separate executables or a single multicall exe doesn't change that it's still a collection of "miniature/cutdown applications". I call these applets.

 

[fr33z0n3r]

You I/O reports 49% using CPU (in a dual core setup this means one core at 100%). Do you have any USB disk plugged in?

Also check dmesg or /tmp/syslog.log for any error message.

I do not have any usb plugged in.

I'll keep the top command info in mind for next time.

Thanks all! No cpu issue as of yet on the current release.

 

[sfx2000]

You I/O reports 49% using CPU (in a dual core setup this means one core at 100%). Do you have any USB disk plugged in?

Also check dmesg or /tmp/syslog.log for any error message.

Wonder if he's just pushing the thing a bit too hard, and the watchdog is kicking the wifi host process for the 2.4GHz radio..

As OP mentioned, he's got an IPv6 tunnel and OpenVPN also running, and we all know that OVPN can peg a core depending on config/traffic at any given time..

 

[sfx2000]

You probably don't have the same definition of applets as I do. The fact that Busybox can be compiled as a bunch of separate executables or a single multicall exe doesn't change that it's still a collection of "miniature/cutdown applications". I call these applets.

Erm - have to disagree here - the whole purpose of busybox is to reduce the memory footprint, as only one set of ELF headers and the busybox app needs to be loaded into RAM...

The "applets" are c modules that one can select to include in the busybox config when building..

BusyBox - The Swiss Army Knife of Embedded Linux

SYNTAX
busybox <applet> [arguments...]  # or
<applet> [arguments...]          # if symlinked


DESCRIPTION

BusyBox combines tiny versions of many common UNIX utilities into a
single small executable. It provides minimalist replacements for most of
the utilities you usually find in GNU coreutils, util-linux, etc. The
utilities in BusyBox generally have fewer options than their
full-featured GNU cousins; however, the options that are included
provide the expected functionality and behave very much like their GNU
counterparts.

BusyBox has been written with size-optimization and limited resources in
mind. It is also extremely modular so you can easily include or exclude
commands (or features) at compile time. This makes it easy to customize
your embedded systems. To create a working system, just add /dev, /etc,
and a Linux kernel. BusyBox provides a fairly complete POSIX environment
for any small or embedded system.

BusyBox is extremely configurable. This allows you to include only the
components you need, thereby reducing binary size. Run 'make config' or
'make menuconfig' to select the functionality that you wish to enable.
Then run 'make' to compile BusyBox using your configuration.

After the compile has finished, you should use 'make install' to install
BusyBox. This will install the 'bin/busybox' binary, in the target
directory specified by CONFIG_PREFIX. CONFIG_PREFIX can be set when
configuring BusyBox, or you can specify an alternative location at
install time (i.e., with a command line like 'make
CONFIG_PREFIX=/tmp/foo install'). If you enabled any applet installation
scheme (either as symlinks or hardlinks), these will also be installed
in the location pointed to by CONFIG_PREFIX.

 

[fr33z0n3r]

Just as a follow-up I have in fact continued to have wifi drop on my phone, but it could be unrelated. The tablet also indicated a network drop today, but I was busy. I did check a short bit ago and there was no cpu issue on the router.

Could be different issues, but I'll continue to monitor.

 

[Nullity]

Erm - have to disagree here - the whole purpose of busybox is to reduce the memory footprint, as only one set of ELF headers and the busybox app needs to be loaded into RAM...

Yeah. I'm unaware of a busybox implementation that uses multiple binaries, unless you consider multiple file-system hardlinks to each be different binaries.

 

[sfx2000]

Yeah. I'm unaware of a busybox implementation that uses multiple binaries, unless you consider multiple file-system hardlinks to each be different binaries.

it's one binary - jeez... how many times to I have to say this...

 

[Sethr]

My phone started doing some AC drop outs after upgrading to 58. It never did it on Alpha, if that helps.
Whenever I notice it, I go into the phone advanced wifi mode. Since it never lasts more than 20-30 seconds, it rolls over to 2.4.

But I am not ready to blame either the 68W or the phone. Sometimes when it does that other neighbor hoods wi-fi, although weaker, will disappear for a while also.

The only other AC in the neighborhood though, according to the router, is on channel 36; I am on 147. And he is only one bar here, so not an issue.

Since it just started on .58 final, I may go to .59 Alpha1 and see what happens.

 

[RMerlin]

Erm - have to disagree here - the whole purpose of busybox is to reduce the memory footprint, as only one set of ELF headers and the busybox app needs to be loaded into RAM...

The "applets" are c modules that one can select to include in the busybox config when building..

BusyBox - The Swiss Army Knife of Embedded Linux

SYNTAX
busybox <applet> [arguments...]  # or
<applet> [arguments...]          # if symlinkedp

Ok, I was wrong about the ability of compiling as separate exe in my second post(I must have confused it with the option of building a shared library), but my original post where I referred to each module as an "applet" (to which you answered they weren't applets) still stands - even your own quote above from the Busybox website has the word "applet" in it...

 

[kvic]

Erm - have to disagree here - the whole purpose of busybox is to reduce the memory footprint, as only one set of ELF headers and the busybox app needs to be loaded into RAM...

The primary goal is to save disk space in the old days when flash memory was a scarce and precious resource. Nowadays flash is in abundance. Little point still deploying Busybox, especially on high-end devices.

Another reason I won't spend a few hundreds on buying consumer wifi routers.

 

[sfx2000]

The primary goal is to save disk space in the old days when flash memory was a scarce and precious resource. Nowadays flash is in abundance. Little point still deploying Busybox, especially on high-end devices.

Another reason I won't spend a few hundreds on buying consumer wifi routers.

Disk space, perhaps, but Busybox was really about saving RAM space - so even today, that's memory that's available for client state tables, and that's all good..

 

[sfx2000]

Ok, I was wrong about the ability of compiling as separate exe in my second post(I must have confused it with the option of building a shared library), but my original post where I referred to each module as an "applet" (to which you answered they weren't applets) still stands - even your own quote above from the Busybox website has the word "applet" in it...

That's ok - from one view, they're apps/applets, from another - it's all a single binary file... I've just always viewed BusyBox as a single file/executable...