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Subject[RFC] export irq_set/get_affinity() for multiqueue network drivers
Hello,

Is there any way to setup IRQ masks from within a driver? myri10ge
currently relies on an external script (writing in
/proc/irq/*/smp_affinity) to bind each queue/MSI-X to a different
processor. By default, Linux will either:
* round-robin the interrupts (killing the benefit of DCA for instance)
* put all IRQs on the same CPU (killing much of the benefit of multislices)
With more and more drivers using multiqueues, I think we need a nice way
to bind MSI-X from within the drivers. I am not sure what's best, the
attached (untested) patch would just export the existing
irq_set_affinity() and add irq_get_affinity(). Comments?

thanks,
Brice

[PATCH] export irq_set/get_affinity() to modules

Export irq_set_affinity() and add/export irq_get_affinity() so that
network drivers may access MSI-X interrupt masks to bind multiqueues
to different CPUs. Otherwise Linux will either:
* round-robin the interrupts (killing the benefit of DCA, for instance)
* put all IRQs on the same CPU (killing much of the benefit of multislices)

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
---
include/linux/interrupt.h | 3 +++
kernel/irq/manage.c | 15 +++++++++++++++
2 files changed, 18 insertions(+)
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -107,6 +107,7 @@ extern void enable_irq(unsigned int irq);
extern cpumask_t irq_default_affinity;

extern int irq_set_affinity(unsigned int irq, cpumask_t cpumask);
+extern int irq_get_affinity(unsigned int irq, cpumask_t *cpumask);
extern int irq_can_set_affinity(unsigned int irq);
extern int irq_select_affinity(unsigned int irq);

@@ -117,6 +118,8 @@ static inline int irq_set_affinity(unsigned int irq, cpumask_t cpumask)
return -EINVAL;
}

+static inline int irq_get_affinity(unsigned int irq) { return 0; }
+
static inline int irq_can_set_affinity(unsigned int irq)
{
return 0;
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -96,6 +96,21 @@ int irq_set_affinity(unsigned int irq, cpumask_t cpumask)
#endif
return 0;
}
+EXPORT_SYMBOL(irq_set_affinity);
+
+int irq_get_affinity(unsigned int irq, cpumask_t *cpumask)
+{
+ struct irq_desc *desc = irq_desc + irq;
+ cpumask_t *mask = &desc->affinity;
+
+#ifdef CONFIG_GENERIC_PENDING_IRQ
+ if (desc->status & IRQ_MOVE_PENDING)
+ mask = &desc->pending_mask;
+#endif
+ memcpy(cpumask, mask, sizeof(*mask);
+ return 0;
+}
+EXPORT_SYMBOL(irq_get_affinity);

#ifndef CONFIG_AUTO_IRQ_AFFINITY
/*
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