Re: [PATCH 3/3] riscv: add PREEMPT_LAZY support

[Peter Zijlstra]

On Wed, Oct 09, 2024 at 12:50:57PM +0200, Sebastian Andrzej Siewior wrote:
> From: Jisheng Zhang <jszhang@xxxxxxxxxx>
> 
> riscv has switched to GENERIC_ENTRY, so adding PREEMPT_LAZY is as simple
> as adding TIF_NEED_RESCHED_LAZY related definitions and enabling
> ARCH_HAS_PREEMPT_LAZY.
> 
> [bigeasy: Replace old PREEMPT_AUTO bits with new PREEMPT_LAZY ]
> 
> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
> Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
>  arch/riscv/Kconfig                   | 1 +
>  arch/riscv/include/asm/thread_info.h | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 62545946ecf43..3516c58480612 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -39,6 +39,7 @@ config RISCV
>  	select ARCH_HAS_MMIOWB
>  	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>  	select ARCH_HAS_PMEM_API
> +	select ARCH_HAS_PREEMPT_LAZY
>  	select ARCH_HAS_PREPARE_SYNC_CORE_CMD
>  	select ARCH_HAS_PTE_DEVMAP if 64BIT && MMU
>  	select ARCH_HAS_PTE_SPECIAL
> diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
> index 9c10fb180f438..8b5a5ddea4293 100644
> --- a/arch/riscv/include/asm/thread_info.h
> +++ b/arch/riscv/include/asm/thread_info.h
> @@ -107,6 +107,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
>   * - pending work-to-be-done flags are in lowest half-word
>   * - other flags in upper half-word(s)
>   */
> +#define TIF_NEED_RESCHED_LAZY	0       /* Lazy rescheduling needed */
>  #define TIF_NOTIFY_RESUME	1	/* callback before returning to user */
>  #define TIF_SIGPENDING		2	/* signal pending */
>  #define TIF_NEED_RESCHED	3	/* rescheduling necessary */

So for x86 I shuffled the flags around to have the two NEED_RESCHED ones
side-by-side. Not strictly required ofcourse, but...