Does DD-WRT QoS actually work?

The answers on this question are really outdated. Development on the DD-WRT has moved on and QoS through GUI is super stable on latest versions.

I'm currently using DD-WRT v24-sp2 (09/09/11) big, SVN revision 17598M NEWD-2 K2.6 Eko on an ASUS RT-N16, and deployed complete QoS for my local home network without any issues. Even though I'm very familiar with CLI, the Web interface did just fine. Premium/Express/Bulk traffic now is being properly categorized and I have finally solved my issues with VOIP and video streaming when someone starts a download or bittorrent and takes the whole channel.

To test if traffic was being categorized properly I used iperf and checked connections on /proc/net/ip_conntrack while live testing each combination of app and protocol.

Suggest you take a look again; you might be pleasantly surprised. Just make sure you use a recent build. The DD-WRT Wiki has setup instructions.

I do not use DD-WRT, but it seems that getting QoS to work requires some fiddling.

I suggest to read carefully this post : dd-wrt router firmware QoS troubleshooting from October 2010 (although it only shapes outgoing traffic), where the accepted answer describes a recent QoS script that apparently worked for both answerer and poster.

However, the described method sounds quite painful, with workarounds for for DD-WRT bugs, patches and whatever, and even so only applies to outgoing traffic.

So the answer for your question is : QoS under DD-WRT still needs fiddling for it to work. The GUI by itself is not enough, which was at least the case toward the end of 2010. So in your shoes I wouldn't bother moving to DD-WRT. Or at least not because of QoS, because it seems to me that QoS is potentially quite frustrating and an excellent time-waster.

The article What is DD-WRT? (section "Special Versions") says for the paid version :

Currently brainslayer offers a special version of DD-WRT with extended QoS capabilities:

• set maximum bandwidth available per netmask/MAC address (v.24-SP1: even for different vlans)
• set a default rule for any unconfigured netmask/MAC address

So it seems that only the paid version of DD-WRT easily supports QoS.

The article How to limit Up/Down speeds per user w/o paid version describes a tool that "works just great for the purpose of setting upload/download limits for users based on IP or MAC addresses".

You might want to study Toastman's work on QoS under Tomato. Apparently QoS is working there. As far as I know Toastman is managing an apartment building of users, so he has the experience. I never used Tomato without setting QoS up, so I can't say what would happen if I didn't!