On Tue, Feb 16, 2021 at 10:44:00AM -0500, Taylor Blau wrote: > On Tue, Feb 16, 2021 at 09:54:24AM -0500, Jeff King wrote: > > This is all on Linux, of course. Perhaps other systems with slower > > syscalls may be more impacted. > > I timed it on macOS, which (as you know) I don't use for daily > development, but it's a useful testbed from time to time. > > On your branch, 'git check-attr -a' took 193.4ms with O_NOFOLLOW, and > 245.3ms without. After touching every .gitattributes file, those numbers > shot up to 340.9ms and 346.6ms, respectively. > > (All numbers on linux.git, of course). That seems...really weird. Your "after touching every file" case is slightly slower, which is totally expected. But why would the _before_ case be so different? It should have made exactly one extra lstat() call, and replaced a bunch of open(NOFOLLOW) calls with lstat() (and if those were so expensive, we'd have presumably seen it in the "touching every file" case which is running _both_ syscalls). Can you double-check your initial timings? > There isn't an apples-to-apples comparison between my numbers and yours > (since my laptop is much slower than yours), but the relative numbers > are quite clear that only doing a single syscall is worth it in the > non-pathological case. I guess in a sense it doesn't matter that much how macos performs. If it has O_NOFOLLOW, then it's a no-brainer to use it. The bigger question is: how many platforms don't have it, and what are _their_ syscalls like (and are they niche enough that we can accept a small slowdown)? The obvious one we'd care the most about is Windows, but I still hold out hope that there's some equivalent mechanism there we can use. -Peff
