[PATCH v2] RISC-V: Show IPI stats

[Anup Patel <anup@brainfault.org>]

This patch provides arch_show_interrupts() implementation to
show IPI stats via /proc/interrupts.

Now the contents of /proc/interrupts" will look like below:
           CPU0       CPU1       CPU2       CPU3
  8:         17          7          6         14  SiFive PLIC   8  virtio0
 10:         10         10          9         11  SiFive PLIC  10  ttyS0
IPI0:       170        673        251         79  Rescheduling interrupts
IPI1:         1         12         27          1  Function call interrupts
IPI2:         0          0          0          0  CPU wake-up interrupts

Signed-off-by: Anup Patel <anup@brainfault.org>
---

Changes since v1:
 - Add stub inline show_ipi_stats() function for !CONFIG_SMP
 - Make ipi_names[] dynamically sized at compile time
 - Minor beautification of ipi_names[] using tabs

 arch/riscv/include/asm/smp.h |  9 +++++++++
 arch/riscv/kernel/irq.c      |  8 ++++++++
 arch/riscv/kernel/smp.c      | 30 ++++++++++++++++++++++++++++--
 3 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
index 8145b8657d20..37e909c04f47 100644
--- a/arch/riscv/include/asm/smp.h
+++ b/arch/riscv/include/asm/smp.h
@@ -36,6 +36,8 @@ static inline bool can_hotplug_cpu(void)
 static inline void arch_send_call_wakeup_ipi(int cpu) { }
 #endif
 
+struct seq_file;
+
 #ifdef CONFIG_SMP
 
 enum ipi_message_type {
@@ -48,6 +50,9 @@ enum ipi_message_type {
 void send_ipi_message(const struct cpumask *to_whom,
 		      enum ipi_message_type operation);
 
+/* print IPI stats */
+void show_ipi_stats(struct seq_file *p, int prec);
+
 /* SMP initialization hook for setup_arch */
 void __init setup_smp(void);
 
@@ -75,6 +80,10 @@ void boot_sec_cpu(void);
 
 #else
 
+static inline void show_ipi_stats(struct seq_file *p, int prec)
+{
+}
+
 static inline int riscv_hartid_to_cpuid(int hartid)
 {
 	return 0;
diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
index 7e14b0d9a71d..96202139ade5 100644
--- a/arch/riscv/kernel/irq.c
+++ b/arch/riscv/kernel/irq.c
@@ -8,6 +8,8 @@
 #include <linux/interrupt.h>
 #include <linux/irqchip.h>
 #include <linux/irqdomain.h>
+#include <linux/seq_file.h>
+#include <asm/smp.h>
 
 /*
  * Possible interrupt causes:
@@ -24,6 +26,12 @@
  */
 #define INTERRUPT_CAUSE_FLAG	(1UL << (__riscv_xlen - 1))
 
+int arch_show_interrupts(struct seq_file *p, int prec)
+{
+	show_ipi_stats(p, prec);
+	return 0;
+}
+
 asmlinkage void __irq_entry do_IRQ(struct pt_regs *regs, unsigned long cause)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);
diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
index 629456bb6122..70fd1351d6d9 100644
--- a/arch/riscv/kernel/smp.c
+++ b/arch/riscv/kernel/smp.c
@@ -22,6 +22,7 @@
 #include <linux/interrupt.h>
 #include <linux/smp.h>
 #include <linux/sched.h>
+#include <linux/seq_file.h>
 
 #include <asm/sbi.h>
 #include <asm/tlbflush.h>
@@ -29,6 +30,7 @@
 
 /* A collection of single bit ipi messages.  */
 static struct {
+	unsigned long stats[IPI_MAX] ____cacheline_aligned;
 	unsigned long bits ____cacheline_aligned;
 } ipi_data[NR_CPUS] __cacheline_aligned;
 
@@ -61,6 +63,7 @@ int setup_profiling_timer(unsigned int multiplier)
 void riscv_software_interrupt(void)
 {
 	unsigned long *pending_ipis = &ipi_data[smp_processor_id()].bits;
+	unsigned long *stats = ipi_data[smp_processor_id()].stats;
 
 	/* Clear pending IPI */
 	csr_clear(sip, SIE_SSIE);
@@ -75,11 +78,15 @@ void riscv_software_interrupt(void)
 		if (ops == 0)
 			return;
 
-		if (ops & (1 << IPI_RESCHEDULE))
+		if (ops & (1 << IPI_RESCHEDULE)) {
+			stats[IPI_RESCHEDULE]++;
 			scheduler_ipi();
+		}
 
-		if (ops & (1 << IPI_CALL_FUNC))
+		if (ops & (1 << IPI_CALL_FUNC)) {
+			stats[IPI_CALL_FUNC]++;
 			generic_smp_call_function_interrupt();
+		}
 
 		BUG_ON((ops >> IPI_MAX) != 0);
 
@@ -105,6 +112,25 @@ send_ipi_message(const struct cpumask *to_whom, enum ipi_message_type operation)
 	sbi_send_ipi(cpumask_bits(&hartid_mask));
 }
 
+static const char *ipi_names[] = {
+	[IPI_RESCHEDULE]	= "Rescheduling interrupts",
+	[IPI_CALL_FUNC]		= "Function call interrupts",
+	[IPI_CALL_WAKEUP]	= "CPU wake-up interrupts",
+};
+
+void show_ipi_stats(struct seq_file *p, int prec)
+{
+	unsigned int cpu, i;
+
+	for (i = 0; i < IPI_MAX; i++) {
+		seq_printf(p, "%*s%u:%s", prec - 1, "IPI", i,
+			   prec >= 4 ? " " : "");
+		for_each_online_cpu(cpu)
+			seq_printf(p, "%10lu ", ipi_data[cpu].stats[i]);
+		seq_printf(p, " %s\n", ipi_names[i]);
+	}
+}
+
 void arch_send_call_function_ipi_mask(struct cpumask *mask)
 {
 	send_ipi_message(mask, IPI_CALL_FUNC);
-- 
2.17.1