Mark Rutland <mark.rutland@xxxxxxx> writes: > On Tue, Nov 07, 2023 at 01:56:46PM -0800, Ankur Arora wrote: >> What's broken: >> - ARCH_NO_PREEMPT (See patch-45 "preempt: ARCH_NO_PREEMPT only preempts >> lazily") >> - Non-x86 architectures. It's trivial to support other archs (only need >> to add TIF_NEED_RESCHED_LAZY) but wanted to hold off until I got some >> comments on the series. >> (From some testing on arm64, didn't find any surprises.) > > When you say "testing on arm64, didn't find any surprises", I assume you mean > with an additional patch adding TIF_NEED_RESCHED_LAZY? Yeah. And, handling that in the user exit path. > Note that since arm64 doesn't use the generic entry code, that also requires > changes to arm64_preempt_schedule_irq() in arch/arm64/kernel/entry-common.c, to > handle TIF_NEED_RESCHED_LAZY. So, the intent (which got muddied due to this overly large series) was to delay handling TIF_NEED_RESCHED_LAZY until we are about to return to user. I think arm64_preempt_schedule_irq() should only handle TIF_NEED_RESCHED and the _TIF_NEED_RESCHED_LAZY should be handled via _TIF_WORK_MASK and do_notify_resume(). (The design is much clearer in Thomas' PoC: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/) >> - ftrace support for need-resched-lazy is incomplete > > What exactly do we need for ftrace here? Only support for TIF_NEED_RESCHED_LAZY which should be complete. That comment was based on a misreading of the code. Thanks -- ankur
