AC66U B1 - Traditional QoS Download Bandwidth Bug?

HarryMuscle

Occasional Visitor
I'm running Merlin firmware on my AC66U B1 router and I noticed that there seems to be a bug in the Traditional QoS download bandwidth setting. Has anyone else noticed that also? With the User Defined Priorities are all set to 100% for download bandwidths I noticed the following pattern:

Setting Traditional QoS Download Bandwidth to 150 Mbps results in speed tests of around 120 Mbps
Setting it to 160 Mbps results in speed tests of around 140 Mbps
Setting it to 180 Mbps results in speed tests of around 150 Mbps
Setting it to 200 Mbps results in speed tests of around 155 Mbps
Setting it to 220 Mbps results in speed tests of around 165 Mbps
Setting it to 240 Mbps results in speed tests of around 167 Mbps (this one is pushing the limit of my interest connection though so it's probably not accurate)

That means in order to achieve aprox. 150 to 160 Mbps on my 170 Mbps connection I'm using a setting of 200 Mbps. I'm assuming this must be a bug of some sorts, or am I missing something obvious somewhere?

Thanks,
Harry

P.S. I'm running a slightly older version of the firmware (384.17 from 2020) so I'm not sure if this bug still exists in the current firmware, but I'm more curious if others have come across it or if I'm missing something obvious, more so than fixing the issue, since setting the bandwidth to a higher value seems to "fix" the issue.
 

L&LD

Part of the Furniture
That may be a (weak) CPU issue, but the bigger issue is running that ancient firmware.

If you value your network security, you really should update asap.
 

HarryMuscle

Occasional Visitor
That may be a (weak) CPU issue, but the bigger issue is running that ancient firmware.

If you value your network security, you really should update asap.
Yup, turns out it was indeed a CPU issue with CPU 1 at 100% and QoS is single threaded so even though CPU 2 is at 0% it still bottle necks. I switched over to Adaptive QoS which seems significantly less CPU intensive and I'm able to get up to 440 Mbps before I'm once again CPU limited (my connection boosts to around 600 Mbps for about 30+ seconds so I'm able to test higher speeds for short periods of time). The downside is that I no longer get an A+ rating on bufferbloat tests. Adaptive QoS seems less good at dealing with bufferbloat so I'm stuck with an A rating which occasionally drops to a C rating. Possibly time to get a faster and newer router.

Thanks,
Harry
 

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