Re: [PATCH v2 1/2] powerpc: Add preempt lazy support
From: Christophe Leroy <hidden>
Date: 2024-11-26 10:53:06
Also in:
lkml
Le 16/11/2024 à 20:23, Shrikanth Hegde a écrit :
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.
FWIW, there is work in progress on using generic entry/exit for powerpc, if you can help testing it that can help, see https://patchwork.ozlabs.org/project/linuxppc-dev/patch/F0AE0A4571CE3126+20241111031934.1579-2-luming.yu@shingroup.cn/ Christophe
quoted hunk ↗ jump to hunk
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 <redacted> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com> --- 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(-)diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 8094a01974cc..2f625aecf94b 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig@@ -145,6 +145,7 @@ 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_64diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h index 6ebca2996f18..2785c7462ebf 100644 --- a/arch/powerpc/include/asm/thread_info.h +++ b/arch/powerpc/include/asm/thread_info.h@@ -103,6 +103,7 @@ 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 */@@ -122,6 +123,7 @@ 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)@@ -142,9 +144,10 @@ 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 */diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index af62ec974b97..8f4acc55407b 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c@@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs) 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 { /*@@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs) /* 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)