From: Shrikanth Hegde <sshegde@linux.ibm.com> Date: Sun, 17 Nov 2024 00:53:05 +0530 Subject: [PATCH 1/2] powerpc: Add preempt lazy support Define preempt lazy bit for Powerpc. Use bit 9 which is free and within 16 bit range of NEED_RESCHED, so compiler can issue single andi. Since Powerpc doesn't use the generic entry/exit, add lazy check at exit to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for return to kernel. Ran a few benchmarks and db workload on Power10. Performance is close to preempt=none/voluntary. Since Powerpc systems can have large core count and large memory, preempt lazy is going to be helpful in avoiding soft lockup issues. Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Reviewed-by: Ankur Arora <ankur.a.arora@oracle.com> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com> Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com> Link: https://patch.msgid.link/20241116192306.88217-2-sshegde@linux.ibm.com Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/thread_info.h | 9 ++++++--- arch/powerpc/kernel/interrupt.c | 4 ++-- 3 files changed, 9 insertions(+), 5 deletions(-) Index: linux-6.12.8-rt7/arch/powerpc/Kconfig =================================================================== @ linux-6.12.8-rt7/arch/powerpc/Kconfig:148 @ config PPC select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE select ARCH_HAS_PHYS_TO_DMA select ARCH_HAS_PMEM_API + select ARCH_HAS_PREEMPT_LAZY select ARCH_HAS_PTE_DEVMAP if PPC_BOOK3S_64 select ARCH_HAS_PTE_SPECIAL select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64 Index: linux-6.12.8-rt7/arch/powerpc/include/asm/thread_info.h =================================================================== --- linux-6.12.8-rt7.orig/arch/powerpc/include/asm/thread_info.h +++ linux-6.12.8-rt7/arch/powerpc/include/asm/thread_info.h @ linux-6.12.8-rt7/arch/powerpc/Kconfig:106 @ void arch_setup_new_exec(void); #define TIF_PATCH_PENDING 6 /* pending live patching update */ #define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */ #define TIF_SINGLESTEP 8 /* singlestepping active */ +#define TIF_NEED_RESCHED_LAZY 9 /* Scheduler driven lazy preemption */ #define TIF_SECCOMP 10 /* secure computing */ #define TIF_RESTOREALL 11 /* Restore all regs (implies NOERROR) */ #define TIF_NOERROR 12 /* Force successful syscall return */ @ linux-6.12.8-rt7/arch/powerpc/Kconfig:126 @ void arch_setup_new_exec(void); #define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE) #define _TIF_SIGPENDING (1<<TIF_SIGPENDING) #define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED) +#define _TIF_NEED_RESCHED_LAZY (1<<TIF_NEED_RESCHED_LAZY) #define _TIF_NOTIFY_SIGNAL (1<<TIF_NOTIFY_SIGNAL) #define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG) #define _TIF_32BIT (1<<TIF_32BIT) @ linux-6.12.8-rt7/arch/powerpc/Kconfig:147 @ void arch_setup_new_exec(void); _TIF_SYSCALL_EMU) #define _TIF_USER_WORK_MASK (_TIF_SIGPENDING | _TIF_NEED_RESCHED | \ - _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ - _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \ - _TIF_NOTIFY_SIGNAL) + _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_RESUME | \ + _TIF_UPROBE | _TIF_RESTORE_TM | \ + _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL) + #define _TIF_PERSYSCALL_MASK (_TIF_RESTOREALL|_TIF_NOERROR) /* Bits in local_flags */ Index: linux-6.12.8-rt7/arch/powerpc/kernel/interrupt.c =================================================================== --- linux-6.12.8-rt7.orig/arch/powerpc/kernel/interrupt.c +++ linux-6.12.8-rt7/arch/powerpc/kernel/interrupt.c @ linux-6.12.8-rt7/arch/powerpc/Kconfig:188 @ again: ti_flags = read_thread_flags(); while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) { local_irq_enable(); - if (ti_flags & _TIF_NEED_RESCHED) { + if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) { schedule(); } else { /* @ linux-6.12.8-rt7/arch/powerpc/Kconfig:399 @ notrace unsigned long interrupt_exit_ker /* Returning to a kernel context with local irqs enabled. */ WARN_ON_ONCE(!(regs->msr & MSR_EE)); again: - if (IS_ENABLED(CONFIG_PREEMPT)) { + if (IS_ENABLED(CONFIG_PREEMPTION)) { /* Return to preemptible kernel context */ if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) { if (preempt_count() == 0)