[v2,03/15] riscv: misaligned: use on_each_cpu() for scalar misaligned access probing

Commit Message

Clément Léger Feb. 10, 2025, 9:35 p.m. UTC

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 <[e-mail]>
---
 arch/riscv/kernel/traps_misaligned.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

Patch

diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
index 66eef398bad4..eb9157e3af73 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)