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

From: Matheus Tavares <matheus.bernardino@usp.br>
Date: Nov 19, 2020, 04:01 UTC
Message-ID: <20201119040117.67914-1-matheus.bernardino@usp.br>
In-Reply-To: <9c999e38-34db-84bb-3a91-ae2a62b964b5@jeffhostetler.com>

Hi, Jeff

On Mon, Nov 16, 2020 at 12:19 PM Jeff Hostetler <git@jeffhostetler.com> wrote:

Show 5 quoted lines

>
> 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