genirq/core: Introduce struct irq_affinity_desc

The interrupt affinity management uses straight cpumask pointers to convey
the automatically assigned affinity masks for managed interrupts. The core
interrupt descriptor allocation also decides based on the pointer being non
NULL whether an interrupt is managed or not.

Devices which use managed interrupts usually have two classes of
interrupts:

  - Interrupts for multiple device queues
  - Interrupts for general device management

Currently both classes are treated the same way, i.e. as managed
interrupts. The general interrupts get the default affinity mask assigned
while the device queue interrupts are spread out over the possible CPUs.

Treating the general interrupts as managed is both a limitation and under
certain circumstances a bug. Assume the following situation:

 default_irq_affinity = 4..7

So if CPUs 4-7 are offlined, then the core code will shut down the device
management interrupts because the last CPU in their affinity mask went
offline.

It's also a limitation because it's desired to allow manual placement of
the general device interrupts for various reasons. If they are marked
managed then the interrupt affinity setting from both user and kernel space
is disabled.

To remedy that situation it's required to convey more information than the
cpumasks through various interfaces related to interrupt descriptor
allocation.

Instead of adding yet another argument, create a new data structure
'irq_affinity_desc' which for now just contains the cpumask. This struct
can be expanded to convey auxilliary information in the next step.

No functional change, just preparatory work.

[ tglx: Simplified logic and clarified changelog ]

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Dou Liyang <douliyangs@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-pci@vger.kernel.org
Cc: kashyap.desai@broadcom.com
Cc: shivasharan.srikanteshwara@broadcom.com
Cc: sumit.saxena@broadcom.com
Cc: ming.lei@redhat.com
Cc: hch@lst.de
Cc: douliyang1@huawei.com
Link: https://lkml.kernel.org/r/20181204155122.6327-2-douliyangs@gmail.com

1 files changed, 12 insertions, 2 deletions

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index ca397ff40836..c44b7844dc83 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -257,6 +257,14 @@ struct irq_affinity {
 	int	*sets;
 };
 
+/**
+ * struct irq_affinity_desc - Interrupt affinity descriptor
+ * @mask:	cpumask to hold the affinity assignment
+ */
+struct irq_affinity_desc {
+	struct cpumask	mask;
+};
+
 #if defined(CONFIG_SMP)
 
 extern cpumask_var_t irq_default_affinity;
@@ -303,7 +311,9 @@ extern int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m);
 extern int
 irq_set_affinity_notifier(unsigned int irq, struct irq_affinity_notify *notify);
 
-struct cpumask *irq_create_affinity_masks(int nvec, const struct irq_affinity *affd);
+struct irq_affinity_desc *
+irq_create_affinity_masks(int nvec, const struct irq_affinity *affd);
+
 int irq_calc_affinity_vectors(int minvec, int maxvec, const struct irq_affinity *affd);
 
 #else /* CONFIG_SMP */
@@ -337,7 +347,7 @@ irq_set_affinity_notifier(unsigned int irq, struct irq_affinity_notify *notify)
 	return 0;
 }
 
-static inline struct cpumask *
+static inline struct irq_affinity_desc *
 irq_create_affinity_masks(int nvec, const struct irq_affinity *affd)
 {
 	return NULL;