From: Jeff Hostetler <firstname.lastname@example.org> To: Matheus Tavares <email@example.com> Cc: firstname.lastname@example.org, email@example.com Subject: Re: RFC: auto-enabling parallel-checkout on NFS Date: Thu, 19 Nov 2020 09:04:34 -0500 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On 11/18/20 11:01 PM, Matheus Tavares wrote: > Hi, Jeff > > On Mon, Nov 16, 2020 at 12:19 PM Jeff Hostetler <firstname.lastname@example.org> 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 seem to recall back when I was working on this problem that the unzip of each blob was a major pain point. Combine this long delta-chains and each worker would need multiple rounds of read/memmap, unzip, and de-delta before it had the complete blob and could then smudge and write. This makes me wonder if repacking the repo with shorter delta-chains affects the checkout times. And improves the perf when there are more workers. I'm not saying that this is a solution, but rather an experiment to see if it changes anything and maybe adjust our focus. > >> 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. I wasn't really thinking about the 64 workers on 1 core case. I was more thinking about the 64 workers on 64 cores case and wondering if workers were being randomly bounced from core to core and we were thrashing. > > Thanks, > Matheus >
next prev parent reply other threads:[~2020-11-19 14:08 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-15 19:43 Matheus Tavares 2020-11-16 15:19 ` Jeff Hostetler 2020-11-19 4:01 ` Matheus Tavares 2020-11-19 14:04 ` Jeff Hostetler [this message] 2020-11-20 12:10 ` Ævar Arnfjörð Bjarmason 2020-11-23 23:18 ` Geert Jansen 2020-11-19 9:01 ` Ævar Arnfjörð Bjarmason 2020-11-19 14:11 ` Jeff Hostetler 2020-11-23 23:37 ` Geert Jansen 2020-11-24 12:58 ` Ævar Arnfjörð Bjarmason
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