On Wed, May 20, 2020 at 11:04:24AM +0800, Ming Lei wrote: > On Wed, May 20, 2020 at 09:18:23AM +0800, Ming Lei wrote: > > On Tue, May 19, 2020 at 05:30:00PM +0200, Christoph Hellwig wrote: > > > On Tue, May 19, 2020 at 09:54:20AM +0800, Ming Lei wrote: > > > > As Thomas clarified, workqueue hasn't such issue any more, and only other > > > > per CPU kthreads can run until the CPU clears the online bit. > > > > > > > > So the question is if IO can be submitted from such kernel context? > > > > > > What other per-CPU kthreads even exist? > > > > I don't know, so expose to wider audiences. > > One user is io uring with IORING_SETUP_SQPOLL & IORING_SETUP_SQ_AFF, see > io_sq_offload_start(), and it is a IO submission kthread. As far as I can tell that code is buggy, as it still needs to migrate the thread away when the cpu is offlined. This isn't a per-cpu kthread in the sene of having one for each CPU. Jens?
