On Tue 13-02-24 21:45:56, Amir Goldstein wrote: > On Wed, Jan 24, 2024 at 6:20 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > On Wed, Jan 24, 2024 at 6:08 PM Jan Kara <jack@xxxxxxx> wrote: > > > On Tue 16-01-24 14:53:00, Amir Goldstein wrote: > > > > On Tue, Jan 16, 2024 at 2:04 PM Jan Kara <jack@xxxxxxx> wrote: > > > > > > > > > > On Tue 16-01-24 13:32:47, Amir Goldstein wrote: > > > > > > If parent inode is not watching, check for the event in masks of > > > > > > sb/mount/inode masks early to optimize out most of the code in > > > > > > __fsnotify_parent() and avoid calling fsnotify(). > > > > > > > > > > > > Jens has reported that this optimization improves BW and IOPS in an > > > > > > io_uring benchmark by more than 10% and reduces perf reported CPU usage. > > > > > > > > > > > > before: > > > > > > > > > > > > + 4.51% io_uring [kernel.vmlinux] [k] fsnotify > > > > > > + 3.67% io_uring [kernel.vmlinux] [k] __fsnotify_parent > > > > > > > > > > > > after: > > > > > > > > > > > > + 2.37% io_uring [kernel.vmlinux] [k] __fsnotify_parent > > > > > > > > > > > > Reported-and-tested-by: Jens Axboe <axboe@xxxxxxxxx> > > > > > > Link: https://lore.kernel.org/linux-fsdevel/b45bd8ff-5654-4e67-90a6-aad5e6759e0b@xxxxxxxxx/ > > > > > > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> > > > > > > --- > > > > > > > > > > > > Jan, > > > > > > > > > > > > Considering that this change looks like a clear win and it actually > > > > > > the change that you suggested, I cleaned it up a bit and posting for > > > > > > your consideration. > > > > > > > > > > Agreed, I like this. What did you generate this patch against? It does not > > > > > apply on top of current Linus' tree (maybe it needs the change sitting in > > > > > VFS tree - which is fine I can wait until that gets merged)? > > > > > > > > > > > > > Yes, it is on top of Christian's vfs-fixes branch. > > > > > > Merged your improvement now (and I've split off the cleanup into a separate > > > change and dropped the creation of fsnotify_path() which seemed a bit > > > pointless with a single caller). All pushed out. > > > > > > > Jan & Jens, > > Although Jan has already queued this v3 patch with sufficient performance > improvement for Jens' workloads, I got a performance regression report from > kernel robot on will-it-scale microbenchmark (buffered write loop) > on my fan_pre_content patches, so I tried to improve on the existing solution. > > I tried something similar to v1/v2 patches, where the sb keeps accounting > of the number of watchers for specific sub-classes of events. > > I've made two major changes: > 1. moved to counters into a per-sb state object fsnotify_sb_connector > as Christian requested > 2. The counters are by fanotify classes, not by specific events, so they > can be used to answer the questions: > a) Are there any fsnotify watchers on this sb? > b) Are there any fanotify permission class listeners on this sb? > c) Are there any fanotify pre-content (a.k.a HSM) class listeners on this sb? > > I think that those questions are very relevant in the real world, because > a positive answer to (b) and (c) is quite rare in the real world, so the > overhead on the permission hooks could be completely eliminated in > the common case. > > If needed, we can further bisect the class counters per specific painful > events (e.g. FAN_ACCESS*), but there is no need to do that before > we see concrete benchmark results. OK, I think this idea is sound, I'd just be interested whether the 0-day bot (or somebody else) is able to see improvement with this. Otherwise why bother :) > Jan, > > Whenever you have the time, feel free to see if this is a valid direction, > if not for the perf optimization then we are going to need the > fsnotify_sb_connector container for other features as well. So firstly the name fsnotify_sb_connector really confuses me. I'd save "connector" names to fsnotify_mark_connector. Maybe fsnotify_sb_info? Then I dislike how we have to specialcase superblock in quite a few places and add these wrappers and what not. This seems to be mostly caused by the fact that you directly embed fsnotify_mark_connector into fsnotify_sb_info. What if we just put fsnotify_connp_t there? I understand that this will mean one more pointer fetch if there are actually marks attached to the superblock and the event mask matches s_fsnotify_mask. But in that case we are likely to generate the event anyway so the cost of that compared to event generation is negligible? And I'd allocate fsnotify_sb_info on demand from fsnotify_add_mark_locked() which means that we need to pass object pointer (in the form of void *) instead of fsnotify_connp_t to various mark adding functions (and transform it to fsnotify_connp_t only in fsnotify_add_mark_locked() after possibly setting up fsnotify_sb_info). Passing void * around is not great but it should be fairly limited (and actually reduces the knowledge of fsnotify internals outside of the fsnotify core). Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
