Re: [PATCH Dovetail 6.16 v3 2/3] arm64: fpsimd: dovetail: Align with x86 implementation

[Philippe Gerum <rpm@xenomai.org>]

Florian Bezdeka <florian.bezdeka@siemens.com> writes:

> The FPU preemption marker is only accessed from the current task, so
> we can avoid atomic operations. Moving the marker from the low level
> flags to the local (synchronous) flags to make that clear.
>
> Gives us some performance and aligns the arm64 implementation with x86.
> ---
>  arch/arm64/include/asm/thread_info.h | 10 +++++-----
>  arch/arm64/kernel/fpsimd.c           |  7 +++++--
>  2 files changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index 3fb3725fb004..a4405b11189b 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -75,7 +75,6 @@ void arch_setup_new_exec(void);
>  #define TIF_SYSCALL_TRACEPOINT	10	/* syscall tracepoint for ftrace */
>  #define TIF_SECCOMP		11	/* syscall secure computing */
>  #define TIF_SYSCALL_EMU		12	/* syscall emulation active */
> -#define TIF_KERNEL_FP_PREEMPTED	15	/* Dovetail: kernel mode FPSIMD section preempted by OOB */
>  #define TIF_MAYDAY		16	/* Emergency trap pending */
>  #define TIF_RETUSER		17	/* INBAND_TASK_RETUSER is pending */
>  #define TIF_MEMDIE		18	/* is terminating due to OOM killer */
> @@ -141,9 +140,10 @@ void arch_setup_new_exec(void);
>  /*
>   * Local (synchronous) thread flags.
>   */
> -#define _TLF_OOB		0x0001
> -#define _TLF_DOVETAIL		0x0002
> -#define _TLF_OFFSTAGE		0x0004
> -#define _TLF_OOBTRAP		0x0008
> +#define _TLF_OOB			0x0001
> +#define _TLF_DOVETAIL			0x0002
> +#define _TLF_OFFSTAGE			0x0004
> +#define _TLF_OOBTRAP			0x0008
> +#define _TLF_KERNEL_FPU_PREEMPTED	0x0010	/* Dovetail: kernel mode FPSIMD section preempted by OOB */
>  
>  #endif /* __ASM_THREAD_INFO_H */
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index aac0dbf6d84e..1f5fcac32b2d 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -2183,7 +2183,7 @@ void fpsimd_suspend_inband(void)
>  	 */
>  	if (test_thread_flag(TIF_KERNEL_FPSTATE)) {
>  		fpsimd_save_state(kfpu);
> -		set_thread_flag(TIF_KERNEL_FP_PREEMPTED);
> +		set_thread_local_flags(_TLF_KERNEL_FPU_PREEMPTED);
>  	}
>  }
>  
> @@ -2191,8 +2191,11 @@ void fpsimd_resume_inband(void)
>  {
>  	struct user_fpsimd_state *kfpu = this_cpu_ptr(&in_kernel_fpstate);
>  
> -	if (test_and_clear_thread_flag(TIF_KERNEL_FP_PREEMPTED))
> +	if (test_thread_local_flags(_TLF_KERNEL_FPU_PREEMPTED)) {
>  		fpsimd_load_state(kfpu);
> +		clear_thread_local_flags(_TLF_KERNEL_FPU_PREEMPTED);
> +	}
> +
>  }
>  
>  #endif

Ack.

-- 
Philippe.