Re: [PATCH v3 7/8] riscv: Add parameter for skipping access speed tests

[Geert Uytterhoeven]

Hi Andrew,

On Tue, 4 Mar 2025 at 13:02, Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote:
> Allow skipping scalar and vector unaligned access speed tests. This
> is useful for testing alternative code paths and to skip the tests in
> environments where they run too slowly. All CPUs must have the same
> unaligned access speed.
>
> The code movement is because we now need the scalar cpu hotplug
> callback to always run, so we need to bring it and its supporting
> functions out of CONFIG_RISCV_PROBE_UNALIGNED_ACCESS.
>
> Signed-off-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>

Thanks for your patch, which is now commit aecb09e091dc1433
("riscv: Add parameter for skipping access speed tests") in
v6.15-rc1.

> --- a/arch/riscv/kernel/unaligned_access_speed.c
> +++ b/arch/riscv/kernel/unaligned_access_speed.c

>  static int __init check_unaligned_access_all_cpus(void)
>  {
>         int cpu;
>
> -       if (!check_unaligned_access_emulated_all_cpus())
> +       if (unaligned_scalar_speed_param == RISCV_HWPROBE_MISALIGNED_SCALAR_UNKNOWN &&
> +           !check_unaligned_access_emulated_all_cpus()) {
>                 check_unaligned_access_speed_all_cpus();
> -
> -       if (!has_vector()) {
> +       } else {
> +               pr_info("scalar unaligned access speed set to '%s' by command line\n",
> +                       speed_str[unaligned_scalar_speed_param]);
>                 for_each_online_cpu(cpu)
> -                       per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_MISALIGNED_VECTOR_UNSUPPORTED;
> -       } else if (!check_vector_unaligned_access_emulated_all_cpus() &&
> -                  IS_ENABLED(CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS)) {
> +                       per_cpu(misaligned_access_speed, cpu) = unaligned_scalar_speed_param;
> +       }
> +
> +       if (!has_vector())
> +               unaligned_vector_speed_param = RISCV_HWPROBE_MISALIGNED_VECTOR_UNSUPPORTED;
> +
> +       if (unaligned_vector_speed_param == RISCV_HWPROBE_MISALIGNED_VECTOR_UNKNOWN &&
> +           !check_vector_unaligned_access_emulated_all_cpus() &&
> +           IS_ENABLED(CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS)) {
>                 kthread_run(vec_check_unaligned_access_speed_all_cpus,
>                             NULL, "vec_check_unaligned_access_speed_all_cpus");
> +       } else {
> +               pr_info("vector unaligned access speed set to '%s' by command line\n",
> +                       speed_str[unaligned_vector_speed_param]);
> +               for_each_online_cpu(cpu)
> +                       per_cpu(vector_misaligned_access, cpu) = unaligned_vector_speed_param;
>         }

On RZ/Five:

    vector unaligned access speed set to 'unsupported' by command line

However, this is not set on my command line?

Apparently this can be set using three different methods:
  1. It is the default value in the declaration of vector_misaligned_access,
  2. From the handle_vector_misaligned_load() exception handler,
  3. From the command line.
Hence the current kernel message is rather confusing...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds