Re: [PATCH 6/9] riscv: Fix set up of vector cpu hotplug callback

[Clément Léger]

On 07/02/2025 17:19, Andrew Jones wrote:
> Whether or not we have RISCV_PROBE_VECTOR_UNALIGNED_ACCESS we need to
> set up a cpu hotplug callback to check if we have vector at all,
> since, when we don't have vector, we need to set
> vector_misaligned_access to unsupported rather than leave it the
> default of unknown.
> 
> Fixes: e7c9d66e313b ("RISC-V: Report vector unaligned access speed hwprobe")
> Signed-off-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/kernel/unaligned_access_speed.c | 31 +++++++++++-----------
>  1 file changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
> index c9d3237649bb..d9d4ca1fadc7 100644
> --- a/arch/riscv/kernel/unaligned_access_speed.c
> +++ b/arch/riscv/kernel/unaligned_access_speed.c
> @@ -356,6 +356,20 @@ static void check_vector_unaligned_access(struct work_struct *work __always_unus
>  	per_cpu(vector_misaligned_access, cpu) = speed;
>  }
>  
> +/* Measure unaligned access speed on all CPUs present at boot in parallel. */
> +static int __init vec_check_unaligned_access_speed_all_cpus(void *unused __always_unused)
> +{
> +	schedule_on_each_cpu(check_vector_unaligned_access);
Hey Andrew,

While at it, could you add a comment stating that schedule_on_cpu()
(while documented as really slow) is used due to kernel_vector_begin()
needing interrupts to be enabled ? I stumbled upon that while reworking
misaligned.

Thanks,

Clément

> +
> +	return 0;
> +}
> +#else /* CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS */
> +static int __init vec_check_unaligned_access_speed_all_cpus(void *unused __always_unused)
> +{
> +	return 0;
> +}
> +#endif
> +
>  static int riscv_online_cpu_vec(unsigned int cpu)
>  {
>  	if (!has_vector()) {
> @@ -363,27 +377,16 @@ static int riscv_online_cpu_vec(unsigned int cpu)
>  		return 0;
>  	}
>  
> +#ifdef CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS
>  	if (per_cpu(vector_misaligned_access, cpu) != RISCV_HWPROBE_MISALIGNED_VECTOR_UNKNOWN)
>  		return 0;
>  
>  	check_vector_unaligned_access_emulated(NULL);
>  	check_vector_unaligned_access(NULL);
> -	return 0;
> -}
> -
> -/* Measure unaligned access speed on all CPUs present at boot in parallel. */
> -static int __init vec_check_unaligned_access_speed_all_cpus(void *unused __always_unused)
> -{
> -	schedule_on_each_cpu(check_vector_unaligned_access);
> +#endif
>  
>  	return 0;
>  }
> -#else /* CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS */
> -static int __init vec_check_unaligned_access_speed_all_cpus(void *unused __always_unused)
> -{
> -	return 0;
> -}
> -#endif
>  
>  static int __init check_unaligned_access_all_cpus(void)
>  {
> @@ -409,10 +412,8 @@ static int __init check_unaligned_access_all_cpus(void)
>  	cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "riscv:online",
>  				  riscv_online_cpu, riscv_offline_cpu);
>  #endif
> -#ifdef CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS
>  	cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "riscv:online",
>  				  riscv_online_cpu_vec, NULL);
> -#endif
>  
>  	return 0;
>  }