Comments on: Linux SFQ experimentation

By: Dan Siemon

Dan Siemon — Sat, 23 Jul 2011 14:51:10 +0000

I use an old PC. Kinda power hungry but it makes it a lot easier to test new things.

I’ve been having some PMTU troubles with newer kernels and IPIP tunnels. Once that’s figured out I’ll hopefully do some more experimentation.

By: hechacker1

hechacker1 — Sat, 23 Jul 2011 00:20:14 +0000

Hmmm. Yeah, today I spent a lot of time working with the Tomato 2.6.22 kernel base, and it seems back-porting newer kernel schedulers is a waste of time.

I gave pfifo a shot at back-porting, and even that depends on pervasive kernel changes.

DD-WRT and OpenWRT use 2.6.24/25 kernels, but those are that different from the 2.6.22 base I have.

Sooooo, with that in mind, all I can really do is tweak the perturb and limits.

I’ve set perturb to 15 seconds, and limits to 2 for sfq. That generally works out well for 1Mbit or less uplinks.

I would appreciate a test to see if the newer SFQ fixes the spikes.

It may just be the case that these little SOHO routers are just not the best thing to work with for scheduling, since they are often stuck on old kernels. It would take significant work to update their kernels.

The best solution it seems is some type of small linux computer (wall plug server) that can easily be updated with newer versions.

By: Dan Siemon

Dan Siemon — Fri, 22 Jul 2011 00:22:11 +0000

I never figured out the source of those spikes for certain but I’m pretty sure it wasn’t due to the size of the queue. There’s been some fixes to SFQ in recent kernels. I should try running these tests again to see if it is fixed.

I doubt there is an optimal perturb time but if the latency spikes I observed have been fixed then there probably isn’t much downside to a short interval.

By: hechacker1

hechacker1 — Sun, 03 Jul 2011 20:17:14 +0000

Any thoughts on an optimal perturb time? Or perhaps pfifo with a lower packet limit is the best solution if we want to avoid large spikes in latency?

I’m currently working to compile a custom firmware for WRT54GL routers, using some suggestions you have tested to reduce bufferbloat.

Any input would be helpful.