[llvm-dev] lld and thread over-subscription

[Alex Rosenberg via llvm-dev]

> On Oct 1, 2015, at 10:26 AM, Hal Finkel via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
>> On Thu, Oct 1, 2015 at 9:35 AM, Hal Finkel < hfinkel at anl.gov > wrote:
>> 
>> Hi Rui, et al.,
>> 
>> I was experimenting yesterday with building lld on my POWER7
>> PPC64/Linux machine, and ran into an unfortunate problem. When
>> running the regressions tests under lit, almost all of the tests
>> fail like this:
>> 
>> terminate called after throwing an instance of 'std::system_error'
>> what(): Resource temporarily unavailable
> 
> To provide a data point; my default environment has this:
> 
> $ ulimit -a | grep proc
> max user processes              (-u) 1024
> 
> This machine has 48 cores, so with lit running 48 tests leaves each test with only about 20 available threads, much less than the 48 each test believes it can use.

We've seen a similar failure on OS X running tests in another LLVM project besides lld. Filipe may remember what it was.

I think the potential improvement here should be to lit since it can know the limit and schedule work accordingly.

Alex