lkl: increase the number of irqs

Since we use one irq for each thread and each device, 64/32 irqs is not
enough in some cases.

To increase the number of irqs and avoid too much overhead we use an
indirect approach: the irqs are marked using a bitmap (array of longs)
and a summary of the modified bits is kept in a separate "index" long -
one bit for each sizeof(long). Thus we can support 4096 irqs on 64bit
platforms and 1024 irqs on 32bit platforms.

Whenever an irq is trigger both the array and the index is updated. To
find which irqs were triggered we first search the index and then the
corresponding part of the arrary.

This limits the number of atomic operations to 2 per irq, in the worst
case, for both triggering and checking irqs.

Signed-off-by: Octavian Purdila <tavi@cs.pub.ro>

arch/lkl/include/asm/irq.h

@@ -1,7 +1,8 @@
 #ifndef _ASM_LKL_IRQ_H
 #define _ASM_LKL_IRQ_H
 
-#define NR_IRQS			((int)sizeof(long) * 8)
+#define IRQ_STATUS_BITS		(sizeof(long) * 8)
+#define NR_IRQS			((int)IRQ_STATUS_BITS * IRQ_STATUS_BITS)
 
 #include <uapi/asm/irq.h>
 

arch/lkl/kernel/irq.c

@@ -9,17 +9,48 @@
 #include <asm/irqflags.h>
 #include <asm/host_ops.h>
 
-static unsigned long irq_status;
-static bool irqs_enabled;
+/*
+ * To avoid much overhead we use an indirect approach: the irqs are marked using
+ * a bitmap (array of longs) and a summary of the modified bits is kept in a
+ * separate "index" long - one bit for each sizeof(long). Thus we can support
+ * 4096 irqs on 64bit platforms and 1024 irqs on 32bit platforms.
+ *
+ * Whenever an irq is trigger both the array and the index is updated. To find
+ * which irqs were triggered we first search the index and then the
+ * corresponding part of the arrary.
+ */
+static unsigned long irq_status[NR_IRQS/IRQ_STATUS_BITS];
+static unsigned long irq_index_status;
+
+static inline unsigned long test_and_clear_irq_index_status(void)
+{
+	if (!irq_index_status)
+		return 0;
+	return __sync_fetch_and_and(&irq_index_status, 0);
+}
+
+static inline unsigned long test_and_clear_irq_status(int index)
+{
+	if (!&irq_status[index])
+		return 0;
+	return __sync_fetch_and_and(&irq_status[index], 0);
+}
+
+static inline void set_irq_status(int irq)
+{
+	int index = irq / IRQ_STATUS_BITS;
+	int bit = irq % IRQ_STATUS_BITS;
+
+	__sync_fetch_and_or(&irq_status[index], BIT(bit));
+	__sync_fetch_and_or(&irq_index_status, BIT(index));
+}
 
-#define TEST_AND_CLEAR_IRQ_STATUS(x)	__sync_fetch_and_and(&irq_status, 0)
-#define IRQ_BIT(x)			BIT(x-1)
-#define SET_IRQ_STATUS(x)		__sync_fetch_and_or(&irq_status, BIT(x - 1))
 
 static struct irq_info {
 	const char *user;
 } irqs[NR_IRQS];
 
+
 /**
  * DO NOT run any linux calls (e.g. printk) here as they may race with the
  * existing linux threads.
@@ -29,34 +60,42 @@ int lkl_trigger_irq(int irq)
 	if (!irq || irq > NR_IRQS)
 		return -EINVAL;
 
-	SET_IRQ_STATUS(irq);
+	set_irq_status(irq);
 
 	wakeup_cpu();
 
 	return 0;
 }
 
-static void run_irqs(void)
+static inline void for_each_bit(unsigned long word, void (*f)(int, int), int j)
 {
-	int i = 1;
-	unsigned long status;
-
-	if (!irq_status)
-		return;
-
-	status = TEST_AND_CLEAR_IRQ_STATUS(IRQS_MASK);
+	int i = 0;
 
-	while (status) {
-		if (status & 1) {
-			irq_enter();
-			generic_handle_irq(i);
-			irq_exit();
-		}
-		status = status >> 1;
+	while (word) {
+		if (word & 1)
+			f(i, j);
+		word >>= 1;
 		i++;
 	}
 }
 
+static inline void deliver_irq(int bit, int index)
+{
+	irq_enter();
+	generic_handle_irq(index * IRQ_STATUS_BITS + bit);
+	irq_exit();
+}
+
+static inline void check_irq_status(int i, int unused)
+{
+	for_each_bit(test_and_clear_irq_status(i), deliver_irq, i);
+}
+
+static void run_irqs(void)
+{
+	for_each_bit(test_and_clear_irq_index_status(), check_irq_status, 0);
+}
+
 int show_interrupts(struct seq_file *p, void *v)
 {
 	return 0;
@@ -89,6 +128,8 @@ void lkl_put_irq(int i, const char *user)
 	irqs[i].user = NULL;
 }
 
+static bool irqs_enabled;
+
 unsigned long arch_local_save_flags(void)
 {
 	return irqs_enabled;