Re: RFC: auto-enabling parallel-checkout on NFS

[Matheus Tavares <matheus.bernardino@usp.br>]

Hi, Jeff

On Mon, Nov 16, 2020 at 12:19 PM Jeff Hostetler <git@jeffhostetler.com> wrote:
>
> I can't really speak to NFS performance, but I have to wonder if there's
> not something else affecting the results -- 4 and/or 8 core results are
> better than 16+ results in some columns.  And we get diminishing returns
> after ~16.

Yeah, that's a good point. I'm not sure yet what's causing the
diminishing returns, but Geert and I are investigating. Maybe we are
hitting some limit for parallelism in this scenario.

> I'm wondering if during these test runs, you were IO vs CPU bound and if
> VM was a problem.

I would say we are more IO bound during these tests. While a sequential
linux-v5.8 checkout usually uses 100% of one core in my laptop's SSD,
in this setup, it only used 5% to 10%. And even with 64 workers (on a
single core), CPU usage stays around 60% most of the time.

About memory, the peak PSS was around 1.75GB, with 64 workers, and the
machine has 10GB of RAM. But are there other numbers that I should keep
an eye on while running the test?

> I'm wondering if setting thread affinity would help here.

Hmm, I only had one core online during the benchmark, so I think thread
affinity wouldn't impact the runtime.

Thanks,
Matheus