On Thu, Jun 27, 2024 at 6:57 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 27 Jun 2024 at 09:32, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > getdent subtest: > > +4.1 lockref_put_return > > +5.7 lockref_get_not_dead > > +68.0 native_queued_spin_lock_slowpath > > For this getdents load, the main call chains that terminate in the > queued spinlock case seem to be > > .lockref_get_not_dead.__legitimize_path.try_to_unlazy_next.lookup_fast > .lockref_get_not_dead.__legitimize_path.try_to_unlazy.lookup_fast > .lockref_get_not_dead.__legitimize_path.try_to_unlazy.link_path_walk > .dput.terminate_walk.path_openat.do_filp_open > > which is interesting because I would have expected the readdir() code > itself to show up. > > But the proc_pident_readdir profiles have all gone down, presumably > because there's just much fewer of them. That part shows no spinlock > in the profile at all. > > WTH is that benchmark doing? The only readdir that shows up is for > what looks like some /proc filesystem thing. > [snip] [pid 24603] openat(AT_FDCWD, "/proc/146/task/146/ns", O_RDONLY|O_DIRECTORY) = 8 [pid 24603] getdents(1048577, 0x561c7bb02b90, 131072) = -1 EBADF (Bad file descriptor) [pid 24603] getdents(8, 0x561c7bb02b90, 0) = -1 EINVAL (Invalid argument) [pid 24603] getdents(8, 0x561c7bb02b90 /* 12 entries */, 131072) = 328 [pid 24603] getdents(8, 0x561c7bb02b90 /* 0 entries */, 131072) = 0 [pid 24603] close(8) = 0 [/snip] Calls with EBADF and EINVAL show up on my debian version and also on the version I compiled from their repo (https://github.com/ColinIanKing/stress-ng.git). This runs over this collection: ret = stress_getdents_rand(args, "/proc", true, 8, bad_fd, &duration, &count); if (ret == -ENOSYS) break; ret = stress_getdents_rand(args, "/dev", true, 1, bad_fd, &duration, &count); if (ret == -ENOSYS) break; ret = stress_getdents_rand(args, "/tmp", true, 4, bad_fd, &duration, &count); if (ret == -ENOSYS) break; ret = stress_getdents_rand(args, "/sys", true, 8, bad_fd, &duration, &count); if (ret == -ENOSYS) break; ret = stress_getdents_rand(args, "/run", true, 2, bad_fd, &duration, &count); if (ret == -ENOSYS) break; hence weird stuff mutex and rwsem stuff as well. All in all I don't think this is a legitimate benchmark per se, but it may be it is doing something similar to what a real workload would do elsewhere with lockref. On that front alone it warrants figuring out (and I am going to sort it out, see my other e-mail). -- Mateusz Guzik <mjguzik gmail.com>
