Web CPU usage doesnt match TOP

[BSOD2600]

Recently Comcast upgraded me to their 105 Mbps tier. Downloading from multiple sources can often max out the router it appears. QoS is configured for 120 / 10 mbps (because when QoS is disabled thats what the comcast speedtest reliably shows). Tonight I noticed was only downloading around 60-70 Mbps. Logged into the router and saw the cpu usage was high. Logged in via SSH and TOP showed very low cpu usage. Not being a Linux admin, am I missing something on how the Web UI calculates cpu utilization?

Screenshot attached:

 

[john9527]

TOP matches.....

0.9% usr
0.1% sys
0.0% nic
19.2% idle
0.0% io
0.5% irq
78.9% sirq

or 100% - 19.2% idle = 80.8% busy
or 0.9% usr + 0.1% sys + 0.0% i0 + 0.5% irq + 78.9% sirq = 80.4% busy

Now, what's causing the high sirq? Are you running any apps or servers on the router?

 

[BSOD2600]

Doh, completely missed the sirq!

No apps or servers I'm aware of.
AiCloud - all disabled
usb apps - none installed

Would that be somehow related to QoS?
There must be a command/tool to dig into the sirq detail?

 

[RMerlin]

TOP matches.....

0.9% usr
0.1% sys
0.0% nic
19.2% idle
0.0% io
0.5% irq
78.9% sirq

or 100% - 19.2% idle = 80.8% busy
or 0.9% usr + 0.1% sys + 0.0% i0 + 0.5% irq + 78.9% sirq = 80.4% busy

Now, what's causing the high sirq? Are you running any apps or servers on the router?

QOS = no CTF. On an RT-AC66U, 150 Mbps is about the max you can achieve without CTF.

 

[BSOD2600]

Interesting. Just the act of having the router web interface open on the home page which shows the cpu usage causes the download speed to drop by ~40 Mbit/s. the drop in the graph shows when I had the page open and then closed. Yes, this time the cpu usage did show near 100% too.

 

[tijaune]

I guess sirq means software interrupt so could be combination of ethernet interface switching and qos done by cpu?

On my rt-ac66u I have slight increase of top sirq also if the real time traffic monitor is opened on the ui (+7 to 10%) but stay around 20%, nowhere near 80%. I also have per IP monitoring activated.