RT AC68U can't achieve more than 600Mbps on latest firmware

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Drake97

New Around Here
Hi,

I have upgraded today from 384.13 to the latest MerlinWRT (386.2_6) and I have noticed a drop in network speed. Before the update, I was able to reach 900Mbps+ speeds on WAN interface without any problem. Now, after the update, it won't pass 600Mbps.
I've also performed a factory reset (because I was also getting a free nvram warning), but that did not help. I've made sure that all "features" that require traffic to pass CPU are disabled: QoS, Traffic Analyzer, Ai Protection, all are turned off.
Also, I have checked in "Tools" > "Sysinfo" and it looks like HW acceleration is enabled. Under "LAN" > "Switch Control" it appears that CTF (Cut Through Forwarding) is enabled (NAT Acceleration: Auto).
I have noticed that, when performing a SpeedTest, the CPU usage jumps to 50-60%, which I don't remember happening on the old firmware.
Is there something I am doing wrong? Would it help if I would flash the firmware using Asus Restoration Utility? Any help is appreciated! Tahnks!
 

Kanji-San

Regular Contributor
Did you run the SpeedTest app, not in the browser!, from a PC connected via Ethernet?
Try also different servers. It depends very much on the server and the time of day.
 

Wisiwyg

Senior Member
Turn off any scripts - Skynet causes me to consistently measure 500-600mb. Turning it off gets me 900+ on a 1gb cable on my AX88U.

And as @Kanji-San noted, don't run speedtest from the router in the browser UI, use a pc with ethernet connection.

This to be expected, not enough CPU on the AC68U to process all that information at 1gb throughput.
 

Drake97

New Around Here
@Kanji-San I have tried from my PC which is nehind the router's NAT (connected via Ethernet).
@Wisiwyg I didn't enable any scripts after I've performed the "Factory Reset". Also, when performing a SpeedTest from the router's Web UI I get speeds like 230-260 Mbps. It's strange, because I remember I got better speeds with the old firmware, so I am afraid of a software issue rather than a hardware one.
 

bennor

Senior Member
... Ai Protection, all are turned off.
In addition to ensuring AIProtection isn't enabled one also has to check the Administration > Privacy section to ensure one has selected Withdraw if there is a Withdraw button on that page. There are, if I remember right, some posts in other Merlin firmware threads indicating that broadband/WAN speed (when doing a speed test) is roughly halved if one doesn't select that Withdraw button after turning off the various options like; AiProtection, Traffic Analyzer, Apps analyzer, Adaptive QoS/Game boost, Web history.
.
 

Adooni

Senior Member
RT-AC68U do not have FA support -if for any reason (like old CFE) you see it in HW acceleration it can be the reason same strange router behavior
you can disable it via putty
Code:
nvram set ctf_fa_cap=0
nvram commit
 

Drake97

New Around Here
After a little more tinkering (rebooting the router many times and enabling/disabling the above mentioned features), it looks like now I can get speeds of 800Mbps which are more like the ones on the old firmware.
Thank you for your help!
 

RMerlin

Asuswrt-Merlin dev
RT-AC68U do not have FA support
It depends on the hardware revision. The initial revision with a bcm4708 (800 MHz) didn't, I believe it was added when they moved to the bcm4709 (the 1+ GHz models).
 

ColinTaylor

Part of the Furniture
The initial revision with a bcm4708 (800 MHz) didn't...
Even there there seems to be some variation. My RT-AC68U with 800MHz CPU has FA. That's not something that I changed because I can see ctf_fa_cap=1 in the CFE (1.0.2.1).
 

RMerlin

Asuswrt-Merlin dev
Even there there seems to be some variation. My RT-AC68U with 800MHz CPU has FA. That's not something that I changed because I can see ctf_fa_cap=1 in the CFE (1.0.2.1).
I'd have to wonder howver if it actually gets enabled, or the nvram variable only acts as a dud. Hard to tell with Broadcom hiding everything as if their company's survival depended on it...
 

ColinTaylor

Part of the Furniture
I'd have to wonder howver if it actually gets enabled, or the nvram variable only acts as a dud. Hard to tell with Broadcom hiding everything as if their company's survival depended on it...
I never worked out what the difference was between CTF and FA from a practical point of view. Is there some kind a test that demonstrates whether one or both of them is in effect? All I know at the moment is that I can max out my ISP download speed of 660 Mbps using a TCP speed test.
 

RMerlin

Asuswrt-Merlin dev
Is there some kind a test that demonstrates whether one or both of them is in effect?
Not that I know of. The firmware first checks if ctf_fa_cap exists (I assume it may be set by the CFE, no idea how the CFE determines the capability however). It it doesn't already exist, then it checks for the presence of /proc/fa to determine if your router is FA capable, and sets the ctf_fa_cap accordingly.

Interestingly enough, my RT-AC66U_B1 is not FA capable, so maybe Asus doesn't just base it on the CPU model, but also on the model itself, where the RT-AC66U_B1 gets FA removed, versus a regular RT-AC68U.

So, I would check if you actually have /proc/fa on your router, chances are if it doesn't exist, then your router lacks FA support.
 

ColinTaylor

Part of the Furniture
Not that I know of. The firmware first checks if ctf_fa_cap exists (I assume it may be set by the CFE, no idea how the CFE determines the capability however). It it doesn't already exist, then it checks for the presence of /proc/fa to determine if your router is FA capable, and sets the ctf_fa_cap accordingly.

Interestingly enough, my RT-AC66U_B1 is not FA capable, so maybe Asus doesn't just base it on the CPU model, but also on the model itself, where the RT-AC66U_B1 gets FA removed, versus a regular RT-AC68U.

So, I would check if you actually have /proc/fa on your router, chances are if it doesn't exist, then your router lacks FA support.
Hmm, seems to be present.
Code:
# strings /dev/mtdblock0 | grep ctf
ctf_fa_cap=1
# ls -l /proc/fa
-r--r--r--    1 admin    root             0 Jun 20 18:32 /proc/fa
# cat /proc/fa
1
I had a look at a few RT-AC68U CFEs that I found online and none of them had ctf_fa_cap in them. Maybe I just got lucky. I think my model was one of the last made before they introduced those with the higher speeds.
Code:
# strings /dev/mtdblock0 | grep clkfreq
clkfreq=800,666
 

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