Re: MirageOS meeting 2024-03-25

[Hannes Mehnert <hannes@xxxxxxxxxxx>]

Hello,

the meeting notes from two weeks ago:

Participants: Magnus, Pierre, Thomas, Vincent, Reynir, Samuel, Romain, 
Hannes, Shakthi
- What do we want Mirage5 to look like? And when do we want to make a 
release? (Thomas)
    - runtime args
        - many changes in mirage tool, so should probably be in next 
release
        - Hannes: would be nice to release this early, could be part of 
ocaml5 - but could also release as 4.x
    - Ocaml 5 support
        - need ocaml5 support, at least single core support in solo5 - 
could release multicore support later
        - Hannes: ocaml5 doesn't need changes in all of mirage? thomas: 
we could separate it, but could also make mirageos5 the ocaml5 release. 
Multicore support will probably require more tooling changes (e.g. if we 
add support for new runtime), could start with single core support in solo5
    - dune pkg?
        - support the new dune pkg system, alpha expected in may
        - Hannes: has already been delayed, so suggest not waiting for 
this. Thomas: should be ready for may this time
        - Romain: dune pkg aims to resolve some of the issues we have 
with opam monorepo, where can we discuss the issues with dune team? 
Thomas: team building and testing packages now, blocker at the moment is 
that packages are required to be relocatable.
        - 
https://github.com/ocaml/dune/issues?q=is%3Aopen+is%3Aissue+milestone%3A%22Package+Management+MVP%22
        - Romain: to clarify the story about cross-compilation, only 
few packages requires it actually and mainly packages with C stubs 
(Zarith, digestif, mirage-crypto). So, we don't systematically need to 
"dunify" all packages (like dbuenzli packages). So it's good that `dune 
pkg` considers packages as a black box package which does not need dune 
to build
        - hannes: Good package to test x-compilation is Zarith/GMP
        - Romain: Zarith/GMP will still need an overlay however 
considering the status of the dunification of this package 
(https://github.com/ocaml/Zarith/pull/143)
    - No more Lwt?
        - larger discussion, may not be able to resolve this now, but 
start discussion
        - Hannes: this could be a separate discussion and will require 
some evaluation as well. Not sure we're ready to move away from this by 
next release. Several alternative schedulers
        - Thomas: Agree it's early, we need to experiment. Currently we 
see that Lwt binds are very slow (see irmin benchmarks, where they 
allocate a lot) so we would like to experiment with alternate solutions 
for Mirage
    - Thomas: ocaml5 support single core + runtime args could be an 
ocaml5 release, then later in the year we could add support for dune pkg 
and multicore support
    - Thomas: will write a suggestion for release candidate and we can 
discuss in two weeks
- PRs:
    - [mirage/mirage#1495](https://github.com/mirage/mirage/pull/1495): 
refactor Dune files
        -  If you have tooling issues (e.g. merlin not working 
properly) please let Thomas know and this could be fixed in this PR
        -  Two conflicting design issues; if you only build a single 
unikernel in a repo then the workflow is ok, but doesn't match mirage 
skeleton - where we build 10 unikernels in one go after configuring each 
of them. Do we want the ability to have multiple unikernels in a single 
repo? Hannes: Never used this, usually build from each directory
- Building MirageOS Library packages on Alpine 3.19 
[Summary](https://hackmd.io/_0QAwb0rS72wDx52hkegPA). Reference: 
https://ocaml.ci.dev/github/mirage CI builds
    - Shakthi: trying to build for alpine in CI, have some patches. Are 
some other distro failures as well. I could start with a subset and fix 
common failures.
    - Thomas: seems to be working in regular CI, should investigate 
what the difference is. Nice to have Alpine support, so upstreaming 
would be good
- MirageOS retreat in Marrakech (Hannes)
    - 18 people signed up!
- Cstruct.t vs bytes/string
    - Hannes: working on removing cstruct in various repositories. E.g. 
mirage-crypto. Result is very nice, we see performance improvements. 
Plan is to remove cstruct in the whole network stack. Not planned in the 
tcp part of mirage-tcpip (as it's very big), but in the other packages 
in the stack. Also tools that use ocaml heap produce more interesting 
results, like statmemprof.
    - Thomas: what type of benchmarks? Hannes: micro benchmarks, 
performance measurements, throughput for symmetric ciphers. No 
improvement for large blocks, but for smaller there is (1024 and less)
- mirage-flow 4.x and shutdown
    - Hannes: added shutdown function so you can close the connection, 
based on initial work from Dave. Have some PRs open, would be nice to 
have reviews. Thomas: Dave will take a look at mirage-tcpip
    - Romain: currently testing tls with shutdown. Works better with http
- Next meeting will be April 8th, same time