[Cake] Cake latency update

Pete Heist peteheist at gmail.com
Sun Feb 12 09:12:01 EST 2017

> On Feb 12, 2017, at 2:08 PM, Dave Taht <dave.taht at gmail.com> wrote:
> Disable offloads on the sky hardware and see what happens?
> ethtool -K gro off tso off gso off your_device

I’d already had them disabled for testing in /etc/network/interfaces:

post-up ethtool -K eth0 tso off gso off gro off sg off

On a whim I tried _enabling_ offloads again but it happens in both cases.

> How old is the OS on that hardware - offloads have always been tricksy.

Pretty new: Ubuntu 16.10 (GNU/Linux 4.8.0-37-generic x86_64)

> as to why you might be seeing it more with cake, with this stuff on,
> you are not necessarily checking every packet for checksums, and flows
> are "finer" - more mixed up packets.
> capturing these events with tcpdump at various points on the path might help.
> Still, these are the kinds of baseline deployment issues that block
> progress elsewhere. The whole first stage of the rocket has to succeed
> in order to test the second. Doesn't matter how good your second stage
> is, if you RUD the first.

It must be a challenge for you guys sometimes! Unless I can find an obvious solution soon it’s probably going to mean a hardware change for me. But there are only a few options I see with what’s available to me now:

1) Using my Apple USB Ethernet adapter for testing instead of just management. Not excited about that- no BQL? USB latency? fq_codel on this adapter over Ethernet reduces Flent RRUL average latency to a pretty solid 1ms, looks sufficient? (Perhaps no coincidence that USB 2.0 start-of-frame is sent every 1 ms.)

2) Using a 1.25 GHz Mac Mini PPC G4 I have laying around. I successfully ran fq_codel for ADSL on that box in the past, but at 5 / 0.5 Mbps. Accurate Flent results running Cake at 80 Mbps? Timer issues? Also I think no BQL support with the Sun GEM chipset: https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/sun/sungem.c <https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/sun/sungem.c>.

3) Using two of these for my routers instead: https://pcengines.ch/alix2d2.htm <https://pcengines.ch/alix2d2.htm>, which I’ll want to test later anyway. They’re not new. 500 MHz AMD Geode LX800. Pre-Obama (June 2008). Not even sure yet if I’ll rate limit properly at 80-90 Mbit with these.

Any opinion on a ‘best’ alternative among these? I’m leaning towards #1 for ease. Otherwise I’ll make my way, and may have to dig up some better hardware.


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