On Fri, May 23, 2025 at 12:19:24PM +0200, Clément Léger wrote:
> schedule_on_each_cpu() was used without any good reason while documented
> as very slow. This call was in the boot path, so better use
> on_each_cpu() for scalar misaligned checking. Vector misaligned check
> still needs to use schedule_on_each_cpu() since it requires irqs to be
> enabled but that's less of a problem since this code is ran in a kthread.
> Add a comment to explicit that.
>
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
> arch/riscv/kernel/traps_misaligned.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index 592b1a28e897..34b4a4e9dfca 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -627,6 +627,10 @@ bool __init check_vector_unaligned_access_emulated_all_cpus(void)
> {
> int cpu;
>
> + /*
> + * While being documented as very slow, schedule_on_each_cpu() is used since
> + * kernel_vector_begin() expects irqs to be enabled or it will panic()
> + */
> schedule_on_each_cpu(check_vector_unaligned_access_emulated);
>
> for_each_online_cpu(cpu)
> @@ -647,7 +651,7 @@ bool __init check_vector_unaligned_access_emulated_all_cpus(void)
>
> static bool unaligned_ctl __read_mostly;
>
> -static void check_unaligned_access_emulated(struct work_struct *work __always_unused)
> +static void check_unaligned_access_emulated(void *arg __always_unused)
> {
> int cpu = smp_processor_id();
> long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu);
> @@ -688,7 +692,7 @@ bool __init check_unaligned_access_emulated_all_cpus(void)
> * accesses emulated since tasks requesting such control can run on any
> * CPU.
> */
> - schedule_on_each_cpu(check_unaligned_access_emulated);
> + on_each_cpu(check_unaligned_access_emulated, NULL, 1);
>
> for_each_online_cpu(cpu)
> if (per_cpu(misaligned_access_speed, cpu)
> --
> 2.49.0
>