[Bloat] DCTCP in linux net-next

Dave Taht dave.taht at gmail.com
Fri Oct 3 11:46:03 EDT 2014

The testing on this DCTCP implementation is documented at:


Very Impressive! The use of classification to run this on the same
data plane as other traffic was clever, also...

Me being me, I'd wanted to test it against fq_codel, codel and pie
(all of which support ECN) instead of RED, test it against competing
cc algorithms (what harm could a cubic sender do in an otherwise dctcp
environment?), all of which were impossible given the age of the patch
prior set.

I had no faith in the prior (pre-bql-era) results for DCTCP.

I am also interested in what effects, if any, sch_fq had on the hosts
vs a vs DCTCP. It looks like the code currently falls back to reno,
not cubic, if ecn is not enabled, also...

There are several tests in netperf-wrapper that could be easily
modified to invoke dctcp instead to very rapidly get that sort of
data. (the tests are things like cubic_reno reno_cubic_westwood_lp and
the various tcp_square_wave tests, the 50 flow test, etc)

Regrettably I'm not in a DC environment, I'm still out here, trying to
fix the edge. Hopefully someone(s) else here will re-run their  tests
in with this modernized version of dctcp....

On Thu, Oct 2, 2014 at 12:58 AM, Daniel Borkmann <dborkman at redhat.com> wrote:
> Hi Dave,
> [ also Cc'ing Florian as co-author ]
> On 10/02/2014 05:20 AM, Dave Taht wrote:
>> I was surprised and delighted to see that DCTCP has now entered the
>> linux net-next kernel (which means it will end up in linux 3.18 if it
>> pans out)...
>> http://thread.gmane.org/gmane.linux.network/332259
>> Benchmarkers fire up yer engines! The last benchmarks of DCTCP were
>> all from the pre-bql era....
> Indeed, please do. ;) We did longer term measurements in a data center
> environment as attached to the commit message, mostly to provoke incast
> collapse. Results were looking quite promising.
>> In similar news, some patches are tightening up BQL. The improvements
>> here are measured in
>> 10s to 100s of us, and in cpu savings...
>> https://patchwork.ozlabs.org/patch/394810/
> Thanks,
> Daniel

Dave Täht


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