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

[Andrew Jones <ajones@ventanamicro.com>]

On Tue, Apr 08, 2025 at 02:25:12PM +0200, Geert Uytterhoeven wrote:
> Hi Andrew,
> 
> On Tue, 4 Mar 2025 at 13:02, Andrew Jones <ajones@ventanamicro.com> 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@ventanamicro.com>
> 
> > --- 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]);
> 
> On SiPEED MAiXBiT, unaligned_scalar_speed_param is zero, and it prints:
> 
>     scalar unaligned access speed set to '(null)' by command line

Thanks, Geert. I think unaligned_scalar_speed_param is likely 1 in this
case and we should be printing 'emulated', but I neglected to add that
string to speed_str[].

I'll fix this too.

Thanks,
drew

> 
> 
> > +               for_each_online_cpu(cpu)
> > +                       per_cpu(vector_misaligned_access, cpu) = unaligned_vector_speed_param;
> >         }
> >
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> -- 
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> 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