[Cake] Cake upstream Planning

Dave Taht dave at taht.net
Thu Nov 16 11:31:24 EST 2017

Pete Heist <peteheist at gmail.com> writes:

>>>    On Nov 15, 2017, at 9:04 PM, Dave Taht <dave at taht.net> wrote:
>>>    Dave Taht <dave at taht.net> writes:
>>>                TCP RTT ~= 8ms with default qdisc, throughput ~= 940 Mbit
>>>            TCP RTT ~= 4.5ms with ‘cake unlimited’, throughput ~= 920 Mbit
>>>            TCP RTT ~= 1ms with ‘cake unlimited lan’, throughput ~= 920 Mbit
>>>    This was with BQL in play? Monitoring BQL's behavior might help.
>>>    I'd also love to know an exact setting for the shaper as a close as
>>>    possible to the underlying bandwidth of ethernet. However, I tend to be
>>>    plagued with
>>> Yes, with BQL (Intel I210 with igb driver on the APU2). An rrul_be test with —
>>> socket-stats.
>> https://github.com/ffainelli/bqlmon was a tool for looking at bql more
>> directly.
>> I had forked it for some reason or another:
>> https://github.com/dtaht/bqlmon
> Nice, that does work for me. It’s interesting that there are four queues for the
> igb driver, 00 - 03, and when I try an rrul_be_nflows test, not all four queues
> are necessarily used. Once I get >= 8 flows in each direction they usually are
> though. I suppose this is the driver deciding when to start using another queue
> or not.

Usually it is selected via a hash. In more than a few cases, however,
the designer of the hardware intended it as a strict priority queue. In
other cases, it's based on the CPU.

In all cases such a limited number of queues tends to cause oddities.

I think it was the mvneta (?) that had the strict priority queue idea baked
into it, which we ended up disabling entirely and going with just one
hardware queue.

> Cake does seem to visibly reduce the size of the queues.

I generally observe that TSO/GRO/etc tends to make BQL's queues 3-5
times larger than they are without those offloads - no way to fix it,
short of doing what cake does to peel those apart.

> For whatever
> terminal/ncurses weirdness reason though, the bar graphs may be sometimes
> blowing off the top of my 45 row screen, but it doesn’t entirely ruin the
> experience.

Maybe that was why I forked it?

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