netdev - [PATCH RFC net-next 1/2] net: napi: add CPU affinity to napi->config

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Message-ID: <20241206001209.213168-2-ahmed.zaki@intel.com>
Date: Thu,  5 Dec 2024 17:12:08 -0700
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: netdev@...r.kernel.org
Cc: Ahmed Zaki <ahmed.zaki@...el.com>,
	Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH RFC net-next 1/2] net: napi: add CPU affinity to napi->config

A common task for most drivers is to remember the user's CPU affinity to
its IRQs. On each netdev reset, the driver must then re-assign the
user's setting to the IRQs.

Add CPU affinity mask to napi->config. To delegate the CPU affinity
management to the core, drivers must:
 1 - add a persistent napi config:     netif_napi_add_config()
 2 - bind an IRQ to the napi instance: netif_napi_set_irq()

the core will then make sure to use re-assign affinity to the napi's
IRQ.

Suggested-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Ahmed Zaki <ahmed.zaki@...el.com>
---
 include/linux/netdevice.h | 22 ++++++++++++++++++++++
 net/core/dev.c            |  7 ++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index ecc686409161..8660de791a1a 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -350,6 +350,7 @@ struct napi_config {
 	u64 gro_flush_timeout;
 	u64 irq_suspend_timeout;
 	u32 defer_hard_irqs;
+	cpumask_t affinity_mask;
 	unsigned int napi_id;
 };
 
@@ -393,6 +394,7 @@ struct napi_struct {
 	int			irq;
 	int			index;
 	struct napi_config	*config;
+	struct irq_affinity_notify affinity_notify;
 };
 
 enum {
@@ -2666,10 +2668,30 @@ static inline void *netdev_priv(const struct net_device *dev)
 void netif_queue_set_napi(struct net_device *dev, unsigned int queue_index,
 			  enum netdev_queue_type type,
 			  struct napi_struct *napi);
+static inline void
+netif_napi_affinity_notify(struct irq_affinity_notify *notify,
+			   const cpumask_t *mask)
+{
+	struct napi_struct *napi =
+		container_of(notify, struct napi_struct, affinity_notify);
+
+	if (napi->config)
+		cpumask_copy(&napi->config->affinity_mask, mask);
+}
+
+static inline void
+netif_napi_affinity_release(struct kref __always_unused *ref) {}
 
 static inline void netif_napi_set_irq(struct napi_struct *napi, int irq)
 {
 	napi->irq = irq;
+
+	if (irq > 0 && napi->config) {
+		napi->affinity_notify.notify = netif_napi_affinity_notify;
+		napi->affinity_notify.release = netif_napi_affinity_release;
+		irq_set_affinity_notifier(irq, &napi->affinity_notify);
+		irq_set_affinity(irq, &napi->config->affinity_mask);
+	}
 }
 
 /* Default NAPI poll() weight
diff --git a/net/core/dev.c b/net/core/dev.c
index 13d00fc10f55..d58779d57994 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6843,6 +6843,8 @@ void __netif_napi_del(struct napi_struct *napi)
 		return;
 
 	if (napi->config) {
+		if (napi->irq > 0)
+			irq_set_affinity_notifier(napi->irq, NULL);
 		napi->index = -1;
 		napi->config = NULL;
 	}
@@ -11184,7 +11186,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 {
 	struct net_device *dev;
 	size_t napi_config_sz;
-	unsigned int maxqs;
+	unsigned int maxqs, i;
 
 	BUG_ON(strlen(name) >= sizeof(dev->name));
 
@@ -11280,6 +11282,9 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 	dev->napi_config = kvzalloc(napi_config_sz, GFP_KERNEL_ACCOUNT);
 	if (!dev->napi_config)
 		goto free_all;
+	for (i = 0; i < maxqs; i++)
+		cpumask_copy(&dev->napi_config[i].affinity_mask,
+			     cpu_online_mask);
 
 	strscpy(dev->name, name);
 	dev->name_assign_type = name_assign_type;
-- 
2.47.0