Date:   Sun, 4 Sep 2022 23:16:12 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Jisheng Zhang <jszhang@...nel.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 4/5] riscv: add lazy preempt support

On Thu, Sep 1, 2022 at 2:08 AM Jisheng Zhang <jszhang@...nel.org> wrote:
>
> Implement the lazy preempt for riscv.
>
> Signed-off-by: Jisheng Zhang <jszhang@...nel.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
>
>
> --
> kvm-riscv mailing list
> kvm-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kvm-riscv



-- 
Best Regards
 Guo Ren

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