Re: [PATCH v3 05/17] riscv: misaligned: use on_each_cpu() for scalar misaligned access probing

Clément Léger
2025-03-14T11:44:08Z

On 13/03/2025 13:57, Andrew Jones wrote:
> On Mon, Mar 10, 2025 at 04:12:12PM +0100, 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>
>> ---
>> arch/riscv/kernel/traps_misaligned.c | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
>> index 90ac74191357..ffac424faa88 100644
>> --- a/arch/riscv/kernel/traps_misaligned.c
>> +++ b/arch/riscv/kernel/traps_misaligned.c
>> @@ -616,6 +616,11 @@ bool check_vector_unaligned_access_emulated_all_cpus(void)
>> return false;
>> }
>>
>> + /*
>> + * 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().
>
> which expects

Hum that would yield the following:

"schedule_on_each_cpu() is used since kernel_vector_begin() that is
called inside the vector code 'which' expects irqs to be enabled or it
will panic()." which seems wrong as well.

I guess something like this would be better:

"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()"

Thanks,

Clément

>
>> + */
>> schedule_on_each_cpu(check_vector_unaligned_access_emulated);
>>
>> for_each_online_cpu(cpu)
>> @@ -636,7 +641,7 @@ bool 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);
>> @@ -677,7 +682,7 @@ bool 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)
>> --
>> 2.47.2
>>
>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>