[PATCH 2/5] irqchip/riscv-imsic: Add a threshold to ext irq handling times

Xu Lu
2025-01-13T15:52:59Z

RISC-V's external irq has higher priority than software irq, timer irq
and pmu overflow irq. In existing implementation of IMSIC driver, If
external irqs keep arriving within a certain period of time, no other
interrupt will get a chance to be handled.

This commit solves this problem by introducing a threshold to the number
of times imsic interrupts can be processed in each round.

Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
---
drivers/irqchip/irq-riscv-imsic-early.c | 31 ++++++++++++++-----------
1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/drivers/irqchip/irq-riscv-imsic-early.c b/drivers/irqchip/irq-riscv-imsic-early.c
index c5c2e6929a2f..63097f2bbadf 100644
--- a/drivers/irqchip/irq-riscv-imsic-early.c
+++ b/drivers/irqchip/irq-riscv-imsic-early.c
@@ -20,6 +20,8 @@

#include "irq-riscv-imsic-state.h"

+#define IMSIC_HANDLE_THRESHOLD 20
+
static int imsic_parent_irq;

#ifdef CONFIG_SMP
@@ -76,6 +78,7 @@ static void imsic_handle_irq(struct irq_desc *desc)
int err, cpu = smp_processor_id();
struct imsic_vector *vec;
unsigned long local_id;
+ unsigned int handled = 0;

chained_irq_enter(chip, desc);

@@ -85,21 +88,23 @@ static void imsic_handle_irq(struct irq_desc *desc)
if (local_id == IMSIC_IPI_ID) {
if (IS_ENABLED(CONFIG_SMP))
ipi_mux_process();
- continue;
- }
-
- if (unlikely(!imsic->base_domain))
- continue;
-
- vec = imsic_vector_from_local_id(cpu, local_id);
- if (!vec) {
- pr_warn_ratelimited("vector not found for local ID 0x%lx\n", local_id);
- continue;
+ } else if (likely(imsic->base_domain)) {
+ vec = imsic_vector_from_local_id(cpu, local_id);
+
+ if (unlikely(!vec))
+ pr_warn_ratelimited("vector not found for local ID 0x%lx\n",
+ local_id);
+ else {
+ err = generic_handle_domain_irq(imsic->base_domain, vec->hwirq);
+
+ if (unlikely(err))
+ pr_warn_ratelimited("hwirq 0x%x mapping not found\n",
+ vec->hwirq);
+ }
}

- err = generic_handle_domain_irq(imsic->base_domain, vec->hwirq);
- if (unlikely(err))
- pr_warn_ratelimited("hwirq 0x%x mapping not found\n", vec->hwirq);
+ if (handled++ >= IMSIC_HANDLE_THRESHOLD)
+ break;
}

chained_irq_exit(chip, desc);
--
2.20.1