[cfe-dev] icecream - what should /proc/cpuinfo contain on remote machines?

[Reid Kleckner via cfe-dev]

This seems like an LLVM bug. I'd rather LLVM didn't look in /proc, but I
can't find an alternative. In any case, we shouldn't print to stderr for a
successful build. Silently falling back to
std::thread::hardware_concurrency() seems fine, which is what the code does.

On Wed, May 10, 2017 at 12:21 PM, Miller Henry via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

>
> Greetings, I’m the maintainer of icecream, and I’m trying to solve a bug
> some of my users are seeing: when using clang  4.0 their build fails
> because the file /proc/cpuinfo does not exist.  I’m trying to figure out
> what the right solution to this is. See
> *https://github.com/icecc/icecream/issues/176*
> <https://github.com/icecc/icecream/issues/176>
> From what we can tell this came in from: *https://reviews.llvm.org/D25564*
> <https://reviews.llvm.org/D25564>.
>
> A summary for those who don’t want to read the above: icecream is a
> distributed build tool that allows you to use other networked computers to
> speed up your builds.  The local build machine where you run “make” ships
> the compiler to remote machines which then run the compiler in a chroot
> (this ensures that if the remote has a different version of clang installed
> we do not use that).
>
> We see three options:
>
> Place an empty /proc/cpuinfo in the chroot. This seems to work and it is
> easy.  From what we can tell this file is only used at link time and
> icecream does not link on remote machines.  However if clang starts to use
> /proc/cpuinfo for something else (asserts on valid contents) we are broke
> again.
>
> When building the compiler package add /proc/cpuinfo from whatever machine
> is building the environment.  /proc/cpuinfo may be bogus but at least it
> exists. This is easy to do, but it is a coincidence if the file is actually
> correct.
>
> Copy /proc/cpuinfo into the chroot on each build machine.  This is the
> most difficult to implement (test), and I’m not sure if it gains anything
> or not. Note in particular that icecream tries hard to use as many cores on
> the remote machines as possible without the user of the remote machine
> noticing a performance problem, thus clang using /proc/cpuinfo to spawn
> additional threads is probably something we do not want.
>
> I’m leaning to the first because it is easy, but others have different
> opinions. After looking at all the responses I’ve concluded that so far
> nobody actually knows enough about what clang is doing (much less planning
> to do) to make a useful decision.  Thus I’m reaching out to the clang
> community: what considerations are we not aware of, and is there a good
> reason to choose any plan?
>
>
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>
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