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

Clément Léger
2025-03-10T15:13:29Z

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() that is called inside the vector code
+ * expects irqs to be enabled or it will panic().
+ */
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