Re: [PATCH v2 4/5] riscv: add lazy preempt support

Guo Ren
2022-09-04T15:16:45Z

On Thu, Sep 1, 2022 at 2:08 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> Implement the lazy preempt for riscv.
>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
> arch/riscv/Kconfig | 1 +
> arch/riscv/include/asm/thread_info.h | 7 +++++--
> arch/riscv/kernel/asm-offsets.c | 1 +
> arch/riscv/kernel/entry.S | 9 +++++++--
> 4 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 7a8134fd7ec9..9f2f1936b1b5 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -105,6 +105,7 @@ config RISCV
> select HAVE_PERF_REGS
> select HAVE_PERF_USER_STACK_DUMP
> select HAVE_POSIX_CPU_TIMERS_TASK_WORK
> + select HAVE_PREEMPT_LAZY
> select HAVE_REGS_AND_STACK_ACCESS_API
> select HAVE_FUNCTION_ARG_ACCESS_API
> select HAVE_STACKPROTECTOR
> diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
> index 78933ac04995..471915b179a2 100644
> --- a/arch/riscv/include/asm/thread_info.h
> +++ b/arch/riscv/include/asm/thread_info.h
> @@ -56,6 +56,7 @@
> struct thread_info {
> unsigned long flags; /* low level flags */
> int preempt_count; /* 0=>preemptible, <0=>BUG */
> + int preempt_lazy_count; /* 0=>preemptible, <0=>BUG */
> /*
> * These stack pointers are overwritten on every system call or
> * exception. SP is also saved to the stack it can be recovered when
> @@ -90,7 +91,7 @@ struct thread_info {
> #define TIF_NOTIFY_RESUME 1 /* callback before returning to user */
> #define TIF_SIGPENDING 2 /* signal pending */
> #define TIF_NEED_RESCHED 3 /* rescheduling necessary */
> -#define TIF_RESTORE_SIGMASK 4 /* restore signal mask in do_signal() */
> +#define TIF_NEED_RESCHED_LAZY 4 /* lazy rescheduling */
> #define TIF_MEMDIE 5 /* is terminating due to OOM killer */
> #define TIF_SYSCALL_TRACEPOINT 6 /* syscall tracepoint instrumentation */
> #define TIF_SYSCALL_AUDIT 7 /* syscall auditing */
> @@ -98,6 +99,7 @@ struct thread_info {
> #define TIF_NOTIFY_SIGNAL 9 /* signal notifications exist */
> #define TIF_UPROBE 10 /* uprobe breakpoint or singlestep */
> #define TIF_32BIT 11 /* compat-mode 32bit process */
> +#define TIF_RESTORE_SIGMASK 12 /* restore signal mask in do_signal() */
>
> #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
> #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
> @@ -108,10 +110,11 @@ struct thread_info {
> #define _TIF_SECCOMP (1 << TIF_SECCOMP)
> #define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL)
> #define _TIF_UPROBE (1 << TIF_UPROBE)
> +#define _TIF_NEED_RESCHED_LAZY (1 << TIF_NEED_RESCHED_LAZY)
>
> #define _TIF_WORK_MASK \
> (_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED | \
> - _TIF_NOTIFY_SIGNAL | _TIF_UPROBE)
> + _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_SIGNAL | _TIF_UPROBE)
>
> #define _TIF_SYSCALL_WORK \
> (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_AUDIT | \
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index df9444397908..e38e33822f72 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -35,6 +35,7 @@ void asm_offsets(void)
> OFFSET(TASK_THREAD_S11, task_struct, thread.s[11]);
> OFFSET(TASK_TI_FLAGS, task_struct, thread_info.flags);
> OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count);
> + OFFSET(TASK_TI_PREEMPT_LAZY_COUNT, task_struct, thread_info.preempt_lazy_count);
> OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);
> OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp);
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index b9eda3fcbd6d..595100a4c2c7 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -361,9 +361,14 @@ restore_all:
> resume_kernel:
> REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
> bnez s0, restore_all
> - REG_L s0, TASK_TI_FLAGS(tp)
> - andi s0, s0, _TIF_NEED_RESCHED
> + REG_L s1, TASK_TI_FLAGS(tp)
> + andi s0, s1, _TIF_NEED_RESCHED
> + bnez s0, 1f
> + REG_L s0, TASK_TI_PREEMPT_LAZY_COUNT(tp)
> + bnez s0, restore_all
> + andi s0, s1, _TIF_NEED_RESCHED_LAZY
Can you tell me, who increased/decreased the PREEMPT_LAZY_COUNT? And
who set NEED_RESCHED_LAZY?

> beqz s0, restore_all
> +1:
> call preempt_schedule_irq
> j restore_all
> #endif
> --
> 2.34.1
>
>
> --
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> kvm-riscv@lists.infradead.org
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--
Best Regards
Guo Ren