Re: [tsvwg] sce vs l4s comparison plots?

Tom Henderson <tomhend@uw.edu> Mon, 11 November 2019 03:31 UTC

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From: Tom Henderson <tomhend@uw.edu>
Date: Sun, 10 Nov 2019 19:31:12 -0800
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Subject: Re: [tsvwg] sce vs l4s comparison plots?
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Dave, responses inline below.
>
>
>>> So far as I know ns(X) does not correctly simulate GSO/TSO even when
>>> run in DCE mode, but I could be out of date on that. TBF (and cake)
>>> do break apart superpackets, htb (+ anything, like fq_codel or dualq)
>>> do not.
>
>
>> Correct, we do not have an ns-3 model for GSO/TSO. Is it needed (in
>> the simulation) if BQL is enabled with small device queues?
>
>
> I don't know. Are you seeing GRO/GSO/TSO superpackets in the path on
> this simulation? It isn't on for a variety of pseudo devices,
> particularly in older releases of linux.

No, neither mode is modeling offload.  My question was about whether,
if BQL is being modeled, and we assume traditional MTU (offload is
off, or offload is on and the packets are split), the resulting pacing
due to BQL is sufficient.  If not, some pointers to recommended ways
to model it would be welcome.

>
> The 4.4 kernel (released 2016-01-10) you are leveraging predates some
> major new network subsystem features, like better pacing, sch_etx, and
> the switch to EDF scheduling (in linux 5.1). I'm sure there are dozens
> more things that might matter, which is why we test. :) I imagine neal
> is more up on all the changes since 4.4 that might matter.

Understood; we are looking for a volunteer to help us with getting
newer kernels enabled in DCE.

- Tom