Hi Peter, This is a follow-up for Lyude's work [1]. Per your feedback at [2], I did some digging and turned out that ARM64 already kinda did this. The basic idea is based on:
1) preempt_count() previously mask our NEED_RESCHED bit, so the effective bits is 31bits 2) with a 64bit preempt count implementation (as in your PREEMPT_LONG proposal), the effective bits that record "whether we CAN preempt or not" still fit in 32bit (i.e. an int) as a result, I don't think we need to change the existing preempt_count() API, but rather keep "32bit vs 64bit" as an implementation detail. This saves us the need to change the printk code for preempt_count(). For people who have reviewed the previous version, patch 8-11 are new, please take a look. The patchset passed the build and booting tests and also a "perf record" test on x86 for NMI code path. I would like to target this changes for 7.2 if possible. [1]: https://lore.kernel.org/all/[email protected]/ [2]: https://lore.kernel.org/all/[email protected]/ Regards, Boqun Boqun Feng (8): preempt: Introduce HARDIRQ_DISABLE_BITS preempt: Introduce __preempt_count_{sub, add}_return() irq & spin_lock: Add counted interrupt disabling/enabling locking: Switch to _irq_{disable,enable}() variants in cleanup guards sched: Remove the unused preempt_offset parameter of __cant_sleep() sched: Avoid signed comparison of preempt_count() in __cant_migrate() preempt: Introduce PREEMPT_COUNT_64BIT arm64: sched/preempt: Enable PREEMPT_COUNT_64BIT Joel Fernandes (1): preempt: Track NMI nesting to separate per-CPU counter Lyude Paul (2): openrisc: Include <linux/cpumask.h> in smp.h irq: Add KUnit test for refcounted interrupt enable/disable arch/arm64/Kconfig | 1 + arch/arm64/include/asm/preempt.h | 18 +++++ arch/openrisc/include/asm/smp.h | 2 + arch/s390/include/asm/preempt.h | 10 +++ arch/x86/Kconfig | 1 + arch/x86/include/asm/preempt.h | 61 +++++++++++---- arch/x86/kernel/cpu/common.c | 2 +- include/asm-generic/preempt.h | 14 ++++ include/linux/hardirq.h | 41 ++++++++-- include/linux/interrupt_rc.h | 63 ++++++++++++++++ include/linux/kernel.h | 4 +- include/linux/preempt.h | 35 ++++++--- include/linux/spinlock.h | 51 +++++++++---- include/linux/spinlock_api_smp.h | 27 +++++++ include/linux/spinlock_api_up.h | 9 +++ include/linux/spinlock_rt.h | 15 ++++ kernel/Kconfig.preempt | 4 + kernel/irq/Makefile | 1 + kernel/irq/refcount_interrupt_test.c | 109 +++++++++++++++++++++++++++ kernel/locking/spinlock.c | 29 +++++++ kernel/sched/core.c | 18 +++-- kernel/softirq.c | 11 +++ lib/locking-selftest.c | 2 +- 23 files changed, 476 insertions(+), 52 deletions(-) create mode 100644 include/linux/interrupt_rc.h create mode 100644 kernel/irq/refcount_interrupt_test.c -- 2.50.1 (Apple Git-155)
