[PATCH] D75153: [ThinLTO] Allow usage of all SMT threads in the system

Thu Apr 16 13:23:25 PDT 2020

aganea added a comment.

In D75153#1987320 <https://reviews.llvm.org/D75153#1987320>, @phosek wrote:

> In D75153#1987272 <https://reviews.llvm.org/D75153#1987272>, @phosek wrote:
>
> > We've started seeing `llvm-cov` on our Linux bots with this error:
> >
> >   terminating with uncaught exception of type std::__2::system_error: thread constructor failed: Resource temporarily unavailable
> >
> >
> > Specifically, we're running `llvm export` which uses `heavyweight_hardware_concurrency` (we use the default number of threads, i.e. `0`): https://github.com/llvm/llvm-project/blob/master/llvm/tools/llvm-cov/CoverageExporterJson.cpp#L169
> >
> > I'm not yet sure what's the problem, but bisecting is pointing at this change.
>
>
> Also on runs that succeeded, we see the execution times more than doubled.

This is caused by a mix of the previous change (rG8404aeb5 <https://reviews.llvm.org/rG8404aeb56a73ab24f9b295111de3b37a37f0b841>, see https://github.com/llvm/llvm-project/commit/8404aeb56a73ab24f9b295111de3b37a37f0b841#diff-9c7f49c15e22d38241ccb9d294f880f4L950) which was restraining the ThreadPool to the number of hardware threads, and this patch which makes the number of threads in the ThreadPool limitless.

I will revert the behavior of `llvm-cov` to previous state, and will check if there are other cases like this.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D75153/new/

https://reviews.llvm.org/D75153