I recently installed luci-app-sqm on my linksys EA4500. I configured the setting as eth0, download 100000 and upload 50000. My queue discipline is set to simple.qos and my link layer is atm at 44 packet overhead.
I noticed that speed since enabling sqm has caused my speed to plummet, before i was getting around 250Mb and now after configuring and enabling sqm my speed is maxing out around 85Mb and I can't seem to get it to go higher no matter how I configure it.
When I disable sqm my speed does go back up to 250Mb but my buffer bloat goes up drastically going straight to an F according to dslreports.
Does anyone have any ideas as to why this might be?
The fact that you get about 85Mb even though you configured 100 suggests that your device is running out of CPU power to run the shapers. Wikidevi suggests you've got 1 core Atheros 720Mhz or thereabouts, so that basically confirms it. For a 250Mbps downlink 50+Mbps uplink with bufferbloat management, you should get a mini x86 PC and don't fool around with other marginal solutions. In the absence of money for that I think maybe Espressobin is your best bet. Certainly something that has at least 1Ghz dual or quad core ARM. You can use your EA4500 as a wifi AP.
Since ADSL tops out around 20Mbps, I seriously doubt you have a 250Mbps link running ATM at all, so the overhead calculation seems wrong. I would guess you use a cable internet link in that case set link layer to ethernet* and overhead to 18 bytes, tcMPU to 64. This will reduce the computational cost of the shaper a tiny bit but it will not allw your router to shape @ 250 Mbps....
) the ATM linklayer will reduce the effective bandwidth by 100-10048/53 = 9.4% to account for the 5 byte per 48 byte payload ATM cell overhead. And since AAL5 insists upon packing each data frame into an integer number of ATM cells, link layer ATM will also incur another bandwidth-loss that depends on the size of each data frame and can range from 0 to almost 50%. In otherwords only set the ATM keyword if your link uses ATM. (And since ATM is on the retreat globally it is most likely than not that your link does not use ATM, with the notable exception of ADSL which still does).
Since I'm fairly new at this the setting I was using were from a tutorial video I found online I figured they weren't accurate but at least a good starting point. I did change the settings to what you recommended and it managed to get my speed up to around 110Mb which seems to a be a decent improvement. My upload buffer bloat went up a bit but that's fine since I rarely upload things.
I'm wondering now if my router can't handle the shapers as suggested by dlakelan.
ssh into the router and run top while you do a speed test from your computer. Watch the %idle stat and see if it goes below 5% if so you may be running out of cpu