[PATCH v2 1/2] powerpc: Add preempt lazy support
Christophe Leroy
christophe.leroy at csgroup.eu
Tue Nov 26 21:53:03 AEDT 2024
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
>
> 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 at linutronix.de>
> Reviewed-by: Ankur Arora <ankur.a.arora at oracle.com>
> Signed-off-by: Shrikanth Hegde <sshegde at 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_64
> diff --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)
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