Gentle ping.
On 2024/6/20 17:00, Jinjie Ruan wrote:
> Enable support for PREEMPT_DYNAMIC on arm32, allowing the preemption model
> to be chosen at boot time.
>
> Similar to arm64, arm32 does not yet use the generic entry code, we must
> define our own `sk_dynamic_irqentry_exit_cond_resched`, which will be
> enabled/disabled by the common code in kernel/sched/core.c.
>
> And arm32 use generic preempt.h, so declare
> `sk_dynamic_irqentry_exit_cond_resched` if the arch do not use generic
> entry. Other architectures which use generic preempt.h but not use generic
> entry can benefit from it.
>
> Test ok with the below cmdline parameters on Qemu versatilepb board:
> `preempt=none`
> `preempt=voluntary`
> `preempt=full`
>
> Update preempt mode with debugfs interface on above Qemu board is also
> tested ok:
> # cd /sys/kernel/debug/sched
> # echo none > preempt
> # echo voluntary > preempt
> # echo full > preempt
>
> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> ---
> arch/arm/Kconfig | 1 +
> arch/arm/include/asm/exception.h | 2 ++
> arch/arm/kernel/Makefile | 2 +-
> arch/arm/kernel/common.c | 13 +++++++++++++
> arch/arm/kernel/entry-armv.S | 7 ++++++-
> include/asm-generic/preempt.h | 5 +++++
> 6 files changed, 28 insertions(+), 2 deletions(-)
> create mode 100644 arch/arm/kernel/common.c
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 036381c5d42f..843f320dde7f 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -124,6 +124,7 @@ config ARM
> select HAVE_PERF_EVENTS
> select HAVE_PERF_REGS
> select HAVE_PERF_USER_STACK_DUMP
> + select HAVE_PREEMPT_DYNAMIC_KEY
> select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
> select HAVE_REGS_AND_STACK_ACCESS_API
> select HAVE_RSEQ
> diff --git a/arch/arm/include/asm/exception.h b/arch/arm/include/asm/exception.h
> index 3c82975d46db..ac96b76b394e 100644
> --- a/arch/arm/include/asm/exception.h
> +++ b/arch/arm/include/asm/exception.h
> @@ -12,4 +12,6 @@
>
> #define __exception_irq_entry __irq_entry
>
> +bool need_irq_preemption(void);
> +
> #endif /* __ASM_ARM_EXCEPTION_H */
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index 89a77e3f51d2..58acd62dc5e9 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -17,7 +17,7 @@ CFLAGS_REMOVE_return_address.o = -pg
>
> # Object file lists.
>
> -obj-y := elf.o entry-common.o irq.o opcodes.o \
> +obj-y := common.o elf.o entry-common.o irq.o opcodes.o \
> process.o ptrace.o reboot.o io.o \
> setup.o signal.o sigreturn_codes.o \
> stacktrace.o sys_arm.o time.o traps.o
> diff --git a/arch/arm/kernel/common.c b/arch/arm/kernel/common.c
> new file mode 100644
> index 000000000000..52b0abcae07e
> --- /dev/null
> +++ b/arch/arm/kernel/common.c
> @@ -0,0 +1,13 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/jump_label.h>
> +#include <asm/exception.h>
> +
> +#ifdef CONFIG_PREEMPT_DYNAMIC
> +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> +
> +bool need_irq_preemption(void)
> +{
> + return static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched);
> +}
> +#endif
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index 6150a716828c..571e86433833 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -221,6 +221,11 @@ __irq_svc:
> irq_handler from_user=0
>
> #ifdef CONFIG_PREEMPTION
> +#ifdef CONFIG_PREEMPT_DYNAMIC
> + bl need_irq_preemption
> + cmp r0, #0
> + beq 2f
> +#endif
> ldr r8, [tsk, #TI_PREEMPT] @ get preempt count
> ldr r0, [tsk, #TI_FLAGS] @ get flags
> teq r8, #0 @ if preempt count != 0
> @@ -228,7 +233,7 @@ __irq_svc:
> tst r0, #_TIF_NEED_RESCHED
> blne svc_preempt
> #endif
> -
> +2:
> svc_exit r5, irq = 1 @ return from exception
> UNWIND(.fnend )
> ENDPROC(__irq_svc)
> diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
> index 51f8f3881523..2db7a3e86303 100644
> --- a/include/asm-generic/preempt.h
> +++ b/include/asm-generic/preempt.h
> @@ -2,6 +2,7 @@
> #ifndef __ASM_PREEMPT_H
> #define __ASM_PREEMPT_H
>
> +#include <linux/jump_label.h>
> #include <linux/thread_info.h>
>
> #define PREEMPT_ENABLED (0)
> @@ -89,6 +90,10 @@ void dynamic_preempt_schedule_notrace(void);
> #define __preempt_schedule() dynamic_preempt_schedule()
> #define __preempt_schedule_notrace() dynamic_preempt_schedule_notrace()
>
> +#ifndef CONFIG_GENERIC_ENTRY
> +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> +#endif
> +
> #else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_KEY*/
>
> #define __preempt_schedule() preempt_schedule()
