On Sun, Jul 31, 2022 at 11:17 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > Thomas Munro <thomas.mu...@gmail.com> writes: > > I noticed this is a 32 bit FBSD system. Is it running on UFS, perhaps > > on slow storage? Are soft updates enabled (visible as options in > > output of "mount")? > > It's an ancient (2006) mac mini with 5400RPM spinning rust. > "mount" says > > /dev/ada0s2a on / (ufs, local, soft-updates, journaled soft-updates) > devfs on /dev (devfs)
I don't have all the details and I may be way off here but I have the impression that when you create and then unlink trees of files quickly, sometimes soft-updates are flushed synchronously, which turns into many 5400 RPM seeks; dtrace could be used to check, but some clues in your numbers would be some kind of correlation between time and number of clusters that are set up and torn down by each test. Without soft-updates, it'd be much worse, because then many more things become synchronous I/O. Even with write caching enabled, soft-updates flush the drive cache when there's a barrier needed for crash safety. It may also be that there is something strange about Apple hardware that makes it extra slow at full-cache-flush operations (cf unexplainable excess slowness of F_FULLFSYNC under macOS including old spinning rust systems and current flash systems, and complaints about this general area on current Apple hardware from the Asahi Linux/M1 port people, though how relevant that is to 2006 spinning rust I dunno). It would be nice to look into how to tune, fix or work around all of that, as it also affects CI which has a IO limits (though admittedly a couple of orders of mag higher IOPS than 5400 RPM).
