[PATCH v5 06/13] riscv: misaligned: use on_each_cpu() for scalar misaligned access probing

Clément Léger
2025-04-17T12:36:15Z

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>
---
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 058a69c30181..fbac0cf1fd30 100644
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -610,6 +610,10 @@ 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)
@@ -630,7 +634,7 @@ 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);
@@ -671,7 +675,7 @@ 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)