[llvm-dev] [GSoC] Community feedback and interest in Distributed lit testing project from 2021 idea list.

James Henderson via llvm-dev llvm-dev at lists.llvm.org
Wed Mar 24 01:26:58 PDT 2021

Hi Soham,

I'm the person who has volunteered to do the GSOC mentoring for this
project, should a suitable person apply for it. I replied to a previous
email on this discussion by a different prospective student (see
https://lists.llvm.org/pipermail/llvm-dev/2021-February/148741.html). You
can find my response in the reply to that email. That response contains a
number of key points about the project and hopefully answers some of your
questions too. There were some comments by other people on this list, with
reference to this topic, in another email thread starting here:

For a concrete use-case, take my company. My 12 core machine takes
somewhere between 20 and 40 minutes to run the entire set of LLVM tests,
depending on what else my machine is doing, and what build configuration I
am running. As we should run these tests prior to committing our changes to
the LLVM main branch, this is a major bottleneck to landing any changes. We
have about 100 computers in the office, and we run an internal distributed
build system, which allows users to distribute their compilations across
many machines, so that rather than having access to just 12 cores, they
have access to 800+ cores potentially, making use of idle resources and
allowing for far more compilations to be done and the result to be produced
faster. If the lit tests could be passed in some way to these machines
(perhaps in batches), the tests would run faster, since you'd have up to
1200 tests running simultaneously, rather than 12. Of course, other
companies will have other distribution systems, so any solution should be
general purpose, and allow individual companies to easily configure things
for their own needs.

A good proposal will show some evidence of an understanding of how lit runs
its tests, how distribution of a large problem like this might be solved,
and some evidence of research into existing distribution systems. It would
also outline how the student plans to tackle the problem, with a rough
breakdown of individual stages and a timeline of how long they estimate
each stage to last. Evidence of any LLVM contributions the student has
already made by the time the proposals have been reviewed will also go a
long way towards helping an application stand out.

I hope that answers your questions, feel free to ask more!


On Wed, 24 Mar 2021 at 03:01, soham dixit <sohamdixit81 at gmail.com> wrote:

> Hello community/Mentor,
> Myself, Soham Dixit an undergraduate student from India. I was
> checking the list of 2021 GSoC projects in LLVM compiler
> infrastructure, and I found 'Distributed lit testing project'[1] as an
> interesting one.
> So far I have built llvm with Clang as a subproject enabled, I have
> tried the `make check*` commands and have tried to see how the
> llvm-lit based tests run.
> AFAIU, there is a bottleneck(mostly time required and the number of
> times we run these regression based tests) for running llvm-lit based
> tests even on pretty good and powerful architectures which I believe
> should be the llvm buildbots(probably).
> Looking into how the building llvm compiler issue was solved mentions
> that the build process was made distributed which might take advantage
> of other nodes in the cluster.
> IIUC, the aim of this project is to follow the similar approach that
> was followed for solving the build problem and this time we are trying
> to parallelize the llvm-lit based tests inside the llvm-lit framework
> to get distributed on nodes in the cluster and collect pass and fail
> results from each node and consolidate the same and represent to the
> developer.
> I am writing this email to get more detailed information about this
> project and see what is the real use case where this project can be
> practically used?
> What is it that I should start looking into to make a good and
> detailed proposal ?
> I have had no experience in compilers but I am interested in getting
> involved.
> Thanks and regards,
> Soham
> [1]https://llvm.org/OpenProjects.html#llvm_distributing_lit
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