On 12/6/23, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Wed, Dec 06, 2023 at 05:30:10PM +0100, Mateusz Guzik wrote: > >> > What the hell is going on? Was ->d_lock on parent serving as a throttle >> > and reducing >> > the access rate to something badly contended down the road? I don't see >> > anything >> > of that sort in the profile changes, though... > >> Not an outlandish claim would be that after you stopped taking one of >> them, spinning went down and more traffic was put on locks which *can* >> put their consumers off cpu (and which *do* do it in this test). > > That's about the only guess I've got (see above), but if that's the case, > which lock would > that be? > >> All that said I think it would help if these reports started including >> off cpu time (along with bt) at least for spawned threads. > Given backtracs I posted it's at least root->kernfs_iattr_rwsem (see kernfs_iop_permission), but there may be more. Ultimately I expect would be easy to answer if one was to rebuild with lockstat. I may end up doing it tomorrow if there is a problem testing this on your end. -- Mateusz Guzik <mjguzik gmail.com>
