Rare project developers

[Alexander Gall <>]

On Fri, 10 Jun 2022 07:26:36 +0200, mc36 <> said:

> On 6/10/22 06:53, mc36 wrote:
>> wait a bit... adding that multi-options stuff is no matter of time to 
>> have...
>> and we still can decide to just use a single set of them....
>> 
> https://bitbucket.software.geant.org/projects/RARE/repos/rare/commits/484fea3b8de9fc091a6a2a2d835924089b48f5ee
> here we goo... i updated r.sh and rp.sh according to the new parameters... 
> also added optimizer1.txt and
> optimizer2.txt for tofino1 and tofino2 use case...

Things are getting even stranger. However, we don't have to deal with
the worst of it, at least not for now. The source of the problem is
that with our current P4 code, optimizations for different values of
RECIR_PORT on Tofino2 can differ significantly (I give an example of a
really nasty case below).

We don't understand why this is so, but luckily we only need one
specific value for RECIR_PORT for Tofino2 and thus we can simply
ignore it.  In fact, we only need two variants of the Tofino2 code if
we want to include support for the Tofino2 model in RARE and a single
variant if we don't:

ASIC:
  CPU_PORT: 0
  RECIT_PORT: 1

Tofino2 model:
  CPU_PORT: 2
  RECIR_PORT: 1

Just as the Tofino model, the Tofino2 model doesn't emulate the CPU
PCIe port but uses the lowest of the CPU Eth ports (i.e. port #2 for
Tofino2 and port #64 for Tofino1).

I have commited these assignments and the Tofino2 optimization for
9.7.2 and all looks good.

Now for the nasty details. First of all, the Tofino2 compiler seems to
be extremely sensitive to even the slightes changes in the code. For
example, your commit
https://bitbucket.software.geant.org/projects/RARE/repos/rare/commits/233cce079794dc91afc5c4d9071fa5ea756f2b65
caused some of the profiles to fail compilation with the optimization
from
https://bitbucket.software.geant.org/projects/RARE/repos/rare/commits/ceda33ac1784d4350ecd417b05a0d864bd45a9fc

This is something to look out for when we push changes in the future
(i.e. that could result in non-compilable code until the optimizer is
run again.

But now to the really bad stuff. Before I committed the changes for
the Tofino2 model, the compilations with and without
-D{DUAL,QUAD}_PIPE differed in the value of RECIR_PORT. I used these
two configurations

-b tofino2 -a t2na
-b tofino2 -a t2na -DQUAD_PIPE

with the GRE profile. The first config optimizes to the values 401408
and 45056. The second config fails to compile with that, so the
optimizer is run again and results in the values 401408, 43520.

Now comes the kicker: the first config does *not* compile with these
lower values! I found that reducing 40140 and 43520 by 5% results in
successful compilation of both configurations. So, a better strategy
than running a full optimization on the second config might be to
reduce the first set of numbers step by step by, say, 1% until all
configurations compile successfully, assuming that the difference
won't be huge.

But, as I said, we don't have to deal with that (yet).

-- 
Alex