x86/irq: Update irq_cfg domain unless the new affinity is a subset of the current domain

Until now, irq_cfg domain is mostly static. Either all CPU's
(used by flat mode) or one CPU (first CPU in the irq afffinity
mask) to which irq is being migrated (this is used by the rest
of apic modes).

Upcoming x2apic cluster mode optimization patch allows the irq
to be sent to any CPU in the x2apic cluster (if supported by the
HW). So irq_cfg domain changes on the fly (depending on which
CPU in the x2apic cluster is online).

Instead of checking for any intersection between the new irq
affinity mask and the current irq_cfg domain, check if the new
irq affinity mask is a subset of the current irq_cfg domain.
Otherwise proceed with updating the irq_cfg domain aswell as
assigning vector's on all the CPUs specified in the new mask.

This also cleans up a workaround in updating irq_cfg domain for
legacy irq's that are handled by the IO-APIC.
Signed-off-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Cc: yinghai@kernel.org
Cc: gorcunov@openvz.org
Cc: agordeev@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1337644682-19854-1-git-send-email-suresh.b.siddha@intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

arch/x86/kernel/apic/io_apic.c

@@ -1126,8 +1126,7 @@ __assign_irq_vector(int irq, struct irq_cfg *cfg, const struct cpumask *mask)
 	old_vector = cfg->vector;
 	if (old_vector) {
 		cpumask_and(tmp_mask, mask, cpu_online_mask);
-		cpumask_and(tmp_mask, cfg->domain, tmp_mask);
-		if (!cpumask_empty(tmp_mask)) {
+		if (cpumask_subset(tmp_mask, cfg->domain)) {
 			free_cpumask_var(tmp_mask);
 			return 0;
 		}
@@ -1141,6 +1140,11 @@ __assign_irq_vector(int irq, struct irq_cfg *cfg, const struct cpumask *mask)
 
 		apic->vector_allocation_domain(cpu, tmp_mask);
 
+		if (cpumask_subset(tmp_mask, cfg->domain)) {
+			free_cpumask_var(tmp_mask);
+			return 0;
+		}
+
 		vector = current_vector;
 		offset = current_offset;
 next:
@@ -1346,13 +1350,6 @@ static void setup_ioapic_irq(unsigned int irq, struct irq_cfg *cfg,
 
 	if (!IO_APIC_IRQ(irq))
 		return;
-	/*
-	 * For legacy irqs, cfg->domain starts with cpu 0 for legacy
-	 * controllers like 8259. Now that IO-APIC can handle this irq, update
-	 * the cfg->domain.
-	 */
-	if (irq < legacy_pic->nr_legacy_irqs && cpumask_test_cpu(0, cfg->domain))
-		apic->vector_allocation_domain(0, cfg->domain);
 
 	if (assign_irq_vector(irq, cfg, apic->target_cpus()))
 		return;