[PATCH] x86_64 irq: reuse vector for __assign_irq_vector

[yhlu <yhlu.kernel@gmail.com>]

in phys flat mode, when using set_xxx_irq_affinity to irq balance from
one cpu to another,  _assign_irq_vector will get to increase last used
vector and get new vector. this will use up the vector if enough
set_xxx_irq_affintiy are called. and end with using same vector in
different cpu for different irq. (that is not what we want, we only
want to use same vector in different cpu for different irq when more
than 0x240 irq needed). To keep it simple, the vector should be reused
instead of getting new vector.

Also according to Eric's review, make it more generic to be used with
flat mode too.

This patch need to be applied over Eric's irq: cpu_online_map patch.


Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Muli Ben-Yehuda <muli@il.ibm.com>
Signed-off-by: Yinghai Lu <yinghai.lu@amd.com>

--- linux-2.6/arch/x86_64/kernel/io_apic.c	2006-10-23 18:44:05.000000000 -0700
+++ linux-2.6.xx/arch/x86_64/kernel/io_apic.c	2006-10-23 18:10:08.000000000 -0700
@@ -613,8 +613,9 @@
 	 * 0x80, because int 0x80 is hm, kind of importantish. ;)
 	 */
 	static int current_vector = FIRST_DEVICE_VECTOR, current_offset = 0;
-	int old_vector = -1;
-	int cpu;
+	int vector = -1, old_vector = -1;
+	cpumask_t domain, new_mask;
+	int cpu, new_cpu;
 
 	BUG_ON((unsigned)irq >= NR_IRQ_VECTORS);
 
@@ -624,15 +625,30 @@
 	if (irq_vector[irq] > 0)
 		old_vector = irq_vector[irq];
 	if (old_vector > 0) {
-		cpus_and(*result, irq_domain[irq], mask);
-		if (!cpus_empty(*result))
-			return old_vector;
+		/* try to reuse vector */
+		for_each_cpu_mask(cpu, mask) {
+			int can_reuse = 1;
+			domain = vector_allocation_domain(cpu);
+			cpus_and(new_mask, domain, cpu_online_map);
+			for_each_cpu_mask(new_cpu, new_mask) {
+				int old_irq;
+				old_irq = per_cpu(vector_irq, new_cpu)[old_vector];
+				if ( (old_irq != irq) && (old_irq != -1)) {
+					can_reuse = 0;
+					break;
+				}
+			}
+
+			if(!can_reuse) continue;
+
+			vector = old_vector;
+			goto found_one;	
+		}
+
 	}
 
 	for_each_cpu_mask(cpu, mask) {
-		cpumask_t domain, new_mask;
-		int new_cpu;
-		int vector, offset;
+		int offset;
 
 		domain = vector_allocation_domain(cpu);
 		cpus_and(new_mask, domain, cpu_online_map);
@@ -656,21 +672,27 @@
 		/* Found one! */
 		current_vector = vector;
 		current_offset = offset;
-		if (old_vector >= 0) {
-			cpumask_t old_mask;
-			int old_cpu;
-			cpus_and(old_mask, irq_domain[irq], cpu_online_map);
-			for_each_cpu_mask(old_cpu, old_mask)
-				per_cpu(vector_irq, old_cpu)[old_vector] = -1;
-		}
-		for_each_cpu_mask(new_cpu, new_mask)
-			per_cpu(vector_irq, new_cpu)[vector] = irq;
-		irq_vector[irq] = vector;
-		irq_domain[irq] = domain;
-		cpus_and(*result, domain, mask);
-		return vector;
+		
+		goto found_one;
 	}
+
 	return -ENOSPC;
+
+found_one:
+	if (old_vector >= 0) {
+		cpumask_t old_mask;
+		int old_cpu;
+		cpus_and(old_mask, irq_domain[irq], cpu_online_map);
+		for_each_cpu_mask(old_cpu, old_mask)
+			per_cpu(vector_irq, old_cpu)[old_vector] = -1;
+	}
+	for_each_cpu_mask(new_cpu, new_mask)
+		per_cpu(vector_irq, new_cpu)[vector] = irq;
+	irq_vector[irq] = vector;
+	irq_domain[irq] = domain;
+	cpus_and(*result, domain, mask);
+	return vector;
+
 }
 
 static int assign_irq_vector(int irq, cpumask_t mask, cpumask_t *result)