[RFC net-next 1/6] netdevice: Add napi_affinity_no_change

[Joe Damato <jdamato@fastly.com>]

Several drivers have their own, very similar, implementations of
determining if IRQ affinity has changed. Create napi_affinity_no_change
to centralize this logic in the core.

This will be used in following commits for various drivers to eliminate
duplicated code.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 include/linux/netdevice.h |  8 ++++++++
 net/core/dev.c            | 14 ++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 0ef3eaa23f4b..dc714a04b90a 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -464,6 +464,14 @@ enum rx_handler_result {
 typedef enum rx_handler_result rx_handler_result_t;
 typedef rx_handler_result_t rx_handler_func_t(struct sk_buff **pskb);
 
+/**
+ * napi_affinity_no_change - determine if CPU affinity changed
+ * @irq: the IRQ whose affinity may have changed
+ *
+ * Return true if the CPU affinity has NOT changed, false otherwise.
+ */
+bool napi_affinity_no_change(unsigned int irq);
+
 void __napi_schedule(struct napi_struct *n);
 void __napi_schedule_irqoff(struct napi_struct *n);
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 751d9b70e6ad..9c56ad49490c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -89,6 +89,7 @@
 #include <linux/errno.h>
 #include <linux/interrupt.h>
 #include <linux/if_ether.h>
+#include <linux/irq.h>
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/ethtool.h>
@@ -6210,6 +6211,19 @@ void __napi_schedule_irqoff(struct napi_struct *n)
 }
 EXPORT_SYMBOL(__napi_schedule_irqoff);
 
+bool napi_affinity_no_change(unsigned int irq)
+{
+	int cpu_curr = smp_processor_id();
+	const struct cpumask *aff_mask;
+
+	aff_mask = irq_get_effective_affinity_mask(irq);
+	if (unlikely(!aff_mask))
+		return true;
+
+	return cpumask_test_cpu(cpu_curr, aff_mask);
+}
+EXPORT_SYMBOL(napi_affinity_no_change);
+
 bool napi_complete_done(struct napi_struct *n, int work_done)
 {
 	unsigned long flags, val, new, timeout = 0;
-- 
2.25.1