netdev - [PATCH v1 net-next 2/6] net: napi: add CPU affinity to napi->config

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Message-ID: <20241210002626.366878-3-ahmed.zaki@intel.com>
Date: Mon,  9 Dec 2024 17:26:22 -0700
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: netdev@...r.kernel.org
Cc: intel-wired-lan@...ts.osuosl.org,
	andrew+netdev@...n.ch,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	davem@...emloft.net,
	michael.chan@...adcom.com,
	tariqt@...dia.com,
	anthony.l.nguyen@...el.com,
	przemyslaw.kitszel@...el.com,
	Ahmed Zaki <ahmed.zaki@...el.com>
Subject: [PATCH v1 net-next 2/6] 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.

The default mask set to all IRQs is all online CPUs.

Suggested-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Ahmed Zaki <ahmed.zaki@...el.com>
---
 include/linux/netdevice.h |  6 ++++++
 net/core/dev.c            | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index b598de335d26..9bf91c3aca8d 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -350,9 +350,14 @@ struct napi_config {
 	u64 gro_flush_timeout;
 	u64 irq_suspend_timeout;
 	u32 defer_hard_irqs;
+	cpumask_t affinity_mask;
 	unsigned int napi_id;
 };
 
+enum {
+	NAPIF_F_IRQ_AFFINITY		= BIT(0)
+};
+
 /*
  * Structure for NAPI scheduling similar to tasklet but with weighting
  */
@@ -394,6 +399,7 @@ struct napi_struct {
 	unsigned long		irq_flags;
 	int			index;
 	struct napi_config	*config;
+	struct irq_affinity_notify affinity_notify;
 };
 
 enum {
diff --git a/net/core/dev.c b/net/core/dev.c
index 6ef9eb401fb2..778ba27d2b83 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6699,11 +6699,35 @@ void netif_queue_set_napi(struct net_device *dev, unsigned int queue_index,
 }
 EXPORT_SYMBOL(netif_queue_set_napi);
 
+static 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 void
+netif_napi_affinity_release(struct kref __always_unused *ref)
+{
+}
+
 static void napi_restore_config(struct napi_struct *n)
 {
 	n->defer_hard_irqs = n->config->defer_hard_irqs;
 	n->gro_flush_timeout = n->config->gro_flush_timeout;
 	n->irq_suspend_timeout = n->config->irq_suspend_timeout;
+
+	if (n->irq > 0 && n->irq_flags & NAPIF_F_IRQ_AFFINITY) {
+		n->affinity_notify.notify = netif_napi_affinity_notify;
+		n->affinity_notify.release = netif_napi_affinity_release;
+		irq_set_affinity_notifier(n->irq, &n->affinity_notify);
+		irq_set_affinity(n->irq, &n->config->affinity_mask);
+	}
+
 	/* a NAPI ID might be stored in the config, if so use it. if not, use
 	 * napi_hash_add to generate one for us. It will be saved to the config
 	 * in napi_disable.
@@ -6720,6 +6744,8 @@ static void napi_save_config(struct napi_struct *n)
 	n->config->gro_flush_timeout = n->gro_flush_timeout;
 	n->config->irq_suspend_timeout = n->irq_suspend_timeout;
 	n->config->napi_id = n->napi_id;
+	if (n->irq > 0 && n->irq_flags & NAPIF_F_IRQ_AFFINITY)
+		irq_set_affinity_notifier(n->irq, NULL);
 	napi_hash_del(n);
 }
 
@@ -11184,7 +11210,7 @@ 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 +11306,9 @@ 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