[Cake] Cake3 - source code and some questions

Adrian Popescu adriannnpopescu at gmail.com
Thu Apr 16 09:48:53 EDT 2015

I've discovered there are other problems in the Linux networking stack
which don't seem to be related to fq_codel, qdiscs, AQM and HTB.

There are latency inducing issues bugs in the Ethernet network drivers
of many network adapters, including e1000e, or in the kernel itself.
Some kernels are better. The newest ones have severe regressions in
this area.

I was under the impression there's a problem in codel or fq_codel that
lead to very frequent latency micro-spikes of between 1 and 3
milliseconds. It also seemed to produce bigger latency spikes under
moderate load. No amount of tuning and disabling of offloads helped
with this.

Imagine having 2 milliseconds of latency to your ISP and having your
router induce between 3 to 5 milliseconds of latency for every flow.
It's not particularly helpful for low latency paths on high bandwidth
links. Adding more latency in both directions to high latency paths is
even worse.

These problems are the reason behind starting this thread. I believed
these problems to be related to fq_codel or to the codel algorithm

My question about porting these improvements to codel and fq_codel was
strictly about the tighter recovery, better invsqrt and other codel
enhancements mentioned on the wiki page.

The solution to this unstable latency will necessitate migration to
another platform without Linux. I'm aware cake and fq_codel won't fix
this problem on Linux.

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