On Mon, May 19, 2025 at 11:25:51AM +0200, Florian Bezdeka wrote: > Hi all, > > sorry for top-posting, but I think it makes sense in this case as I'm > trying to merge different workstreams, likely working on the same > problem showing up in different colors. > > Main goal is to make everybody aware of the other stream / patch > series. > > We have colleagues from Bytedance working on non-RT performance > optimizations related to CONFIG_CFS_BANDWIDTH at [1]. > > This series came to light while searching for a solution for a RT > lockup, reported at [2]. > > We heavily tested [1] during the last month on RT and can report > success now. In our tests we saw read-lock holder preemption only > within the epoll interface. It might be that [1] fixes more potential > issues in this regard. > > Today [3] (= the patch I'm replying to, see below) got posted. > Linutronix reworking the epoll infrastructure. > > I would love to learn how/if the combination, basically [1] and [3] fit > together. [1] fixes stall problem involving rw semaphore which epoll uses, but it doesn't fix the possible priority inversion with epoll [3] fixes priority inversion problem with epoll by stop using rw semaphore, but it doesn't do anything about rw semaphore So I propose we keep both. Best regards, Nam > My understanding right now is, that [1] fixes a CFS issue, throttling > while holding a lock is not ideal on !RT - but might cause a critical > lockup on RT - while [3] is addressing a similar (RT) problem in epoll. > > Best regards, > Florian > > [1] https://lore.kernel.org/all/20250409120746.635476-1-ziqianlu@xxxxxxxxxxxxx/ > [2] https://lore.kernel.org/linux-rt-users/xhsmhttqvnall.mognet@xxxxxxxxxxxxxxxxxxx/ > [3] https://lore.kernel.org/linux-rt-users/20250519074016.3337326-1-namcao@xxxxxxxxxxxxx/T/#u
