On Wed, Nov 08, 2023 at 02:04:02AM -0800, Ankur Arora wrote: > >> Revert "riscv: support PREEMPT_DYNAMIC with static keys" > >> Revert "livepatch,sched: Add livepatch task switching to > >> cond_resched()" > >> Revert "arm64: Support PREEMPT_DYNAMIC" > >> Revert "sched/preempt: Add PREEMPT_DYNAMIC using static keys" > > What's the best way to handle these? With the lazy bit, cond_resched() > and might_resched() are gone. So we don't need all of the static > key inftrastructure for toggling etc. > > The part of preempt_dynamic that makes sense to me is the one that > switches dynamically between none/voluntary/full. Here it would need > to be wired onto controls of the lazy bit. > (Right now the preemption policy is controlled by sched_feat in > patches 43, and 44 but sched/preempt is a much better interface.) I'm not understanding, those should stay obviously. The current preempt_dynamic stuff has 5 toggles: /* * SC:cond_resched * SC:might_resched * SC:preempt_schedule * SC:preempt_schedule_notrace * SC:irqentry_exit_cond_resched * * * NONE: * cond_resched <- __cond_resched * might_resched <- RET0 * preempt_schedule <- NOP * preempt_schedule_notrace <- NOP * irqentry_exit_cond_resched <- NOP * * VOLUNTARY: * cond_resched <- __cond_resched * might_resched <- __cond_resched * preempt_schedule <- NOP * preempt_schedule_notrace <- NOP * irqentry_exit_cond_resched <- NOP * * FULL: * cond_resched <- RET0 * might_resched <- RET0 * preempt_schedule <- preempt_schedule * preempt_schedule_notrace <- preempt_schedule_notrace * irqentry_exit_cond_resched <- irqentry_exit_cond_resched */ If you kill voluntary as we know it today, you can remove cond_resched and might_resched, but the remaining 3 are still needed to switch between NONE and FULL. Additionally, you'll get one new state to enable/disable the LAZY stuff. Neither NONE nor FULL want the LAZY thing on. You'll then end up with something like: /* * SK:preempt_lazy * SC:preempt_schedule * SC:preempt_schedule_notrace * SC:irqentry_exit_cond_resched * * * NONE: * preempt_lazy <- OFF * preempt_schedule <- NOP * preempt_schedule_notrace <- NOP * irqentry_exit_cond_resched <- NOP * * VOLUNTARY: * preempt_lazy <- ON * preempt_schedule <- preempt_schedule * preempt_schedule_notrace <- preempt_schedule_notrace * irqentry_exit_cond_resched <- irqentry_exit_cond_resched * * FULL: * preempt_lazy <- OFF * preempt_schedule <- preempt_schedule * preempt_schedule_notrace <- preempt_schedule_notrace * irqentry_exit_cond_resched <- irqentry_exit_cond_resched */ For the architectures that do not have static_call but instead use static_key for everything, the SC's are obviously static_key based wrappers around the function calls -- like now.
