On Fri, Aug 21, 2020 at 1:58 PM Jeff King <peff@xxxxxxxx> wrote: > So what's a good default value? It's clear that the current cap of 3 is > too low; our default values are 42% and 57% slower than the best times > on each machine. The results on the 40-core machine imply that 20 > threads is an actual barrier regardless of the number of cores, so we'll > take that as a maximum. We get the best results on these machines at > half of the online-cpus value. That's presumably a result of the > hyperthreading. That's common on multi-core Intel processors, but not > necessarily elsewhere. But if we take it as an assumption, we can > perform optimally on hyperthreaded machines and still do much better > than the status quo on other machines, as long as we never half below > the current value of 3. I'm not familiar with the index-pack machinery, so this response may be silly, but the first question which came to my mind was whether or not SSD vs. spinning-platter disk impacts these results, and which of the two you were using for the tests (which I don't think was mentioned in any of the commit messages). So, basically, I'm wondering about the implication of this change for those of us still stuck with old spinning-platter disks.
