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Message-ID: <1386247508.30495.180.camel@edumazet-glaptop2.roam.corp.google.com>
Date: Thu, 05 Dec 2013 04:45:08 -0800
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next] net: introduce dev_consume_skb_any()
From: Eric Dumazet <edumazet@...gle.com>
Some network drivers use dev_kfree_skb_any() and dev_kfree_skb_irq()
helpers to free skbs, both for dropped packets and TX completed ones.
We need to separate the two causes to get better diagnostics
given by dropwatch or "perf record -e skb:kfree_skb"
This patch provides two new helpers, dev_consume_skb_any() and
dev_consume_skb_irq() to be used for consumed skbs.
__dev_kfree_skb_irq() is slightly optimized to remove one
atomic_dec_and_test() in fast path, and use this_cpu_{r|w} accessors.
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
include/linux/netdevice.h | 53 +++++++++++++++++++++++++++++-------
net/core/dev.c | 45 ++++++++++++++++++++----------
2 files changed, 74 insertions(+), 24 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 7f0ed423a360..c6d64d20050c 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2368,17 +2368,52 @@ static inline int netif_copy_real_num_queues(struct net_device *to_dev,
#define DEFAULT_MAX_NUM_RSS_QUEUES (8)
int netif_get_num_default_rss_queues(void);
-/* Use this variant when it is known for sure that it
- * is executing from hardware interrupt context or with hardware interrupts
- * disabled.
- */
-void dev_kfree_skb_irq(struct sk_buff *skb);
+enum skb_free_reason {
+ SKB_REASON_CONSUMED,
+ SKB_REASON_DROPPED,
+};
+
+void __dev_kfree_skb_irq(struct sk_buff *skb, enum skb_free_reason reason);
+void __dev_kfree_skb_any(struct sk_buff *skb, enum skb_free_reason reason);
-/* Use this variant in places where it could be invoked
- * from either hardware interrupt or other context, with hardware interrupts
- * either disabled or enabled.
+/*
+ * It is not allowed to call kfree_skb() or consume_skb() from hardware
+ * interrupt context or with hardware interrupts being disabled.
+ * (in_irq() || irqs_disabled())
+ *
+ * We provide four helpers that can be used in following contexts :
+ *
+ * dev_kfree_skb_irq(skb) when caller drops a packet from irq context,
+ * replacing kfree_skb(skb)
+ *
+ * dev_consume_skb_irq(skb) when caller consumes a packet from irq context.
+ * Typically used in place of consume_skb(skb) in TX completion path
+ *
+ * dev_kfree_skb_any(skb) when caller doesn't know its current irq context,
+ * replacing kfree_skb(skb)
+ *
+ * dev_consume_skb_any(skb) when caller doesn't know its current irq context,
+ * and consumed a packet. Used in place of consume_skb(skb)
*/
-void dev_kfree_skb_any(struct sk_buff *skb);
+static inline void dev_kfree_skb_irq(struct sk_buff *skb)
+{
+ __dev_kfree_skb_irq(skb, SKB_REASON_DROPPED);
+}
+
+static inline void dev_consume_skb_irq(struct sk_buff *skb)
+{
+ __dev_kfree_skb_irq(skb, SKB_REASON_CONSUMED);
+}
+
+static inline void dev_kfree_skb_any(struct sk_buff *skb)
+{
+ __dev_kfree_skb_any(skb, SKB_REASON_DROPPED);
+}
+
+static inline void dev_consume_skb_any(struct sk_buff *skb)
+{
+ __dev_kfree_skb_any(skb, SKB_REASON_CONSUMED);
+}
int netif_rx(struct sk_buff *skb);
int netif_rx_ni(struct sk_buff *skb);
diff --git a/net/core/dev.c b/net/core/dev.c
index ba3b7ea5ebb3..aa54a742f392 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2145,30 +2145,42 @@ void __netif_schedule(struct Qdisc *q)
}
EXPORT_SYMBOL(__netif_schedule);
-void dev_kfree_skb_irq(struct sk_buff *skb)
+struct dev_kfree_skb_cb {
+ enum skb_free_reason reason;
+};
+
+static struct dev_kfree_skb_cb *get_kfree_skb_cb(const struct sk_buff *skb)
+{
+ return (struct dev_kfree_skb_cb *)skb->cb;
+}
+
+void __dev_kfree_skb_irq(struct sk_buff *skb, enum skb_free_reason reason)
{
- if (atomic_dec_and_test(&skb->users)) {
- struct softnet_data *sd;
- unsigned long flags;
+ unsigned long flags;
- local_irq_save(flags);
- sd = &__get_cpu_var(softnet_data);
- skb->next = sd->completion_queue;
- sd->completion_queue = skb;
- raise_softirq_irqoff(NET_TX_SOFTIRQ);
- local_irq_restore(flags);
+ if (likely(atomic_read(&skb->users) == 1)) {
+ smp_rmb();
+ atomic_set(&skb->users, 0);
+ } else if (likely(!atomic_dec_and_test(&skb->users))) {
+ return;
}
+ get_kfree_skb_cb(skb)->reason = reason;
+ local_irq_save(flags);
+ skb->next = __this_cpu_read(softnet_data.completion_queue);
+ __this_cpu_write(softnet_data.completion_queue, skb);
+ raise_softirq_irqoff(NET_TX_SOFTIRQ);
+ local_irq_restore(flags);
}
-EXPORT_SYMBOL(dev_kfree_skb_irq);
+EXPORT_SYMBOL(__dev_kfree_skb_irq);
-void dev_kfree_skb_any(struct sk_buff *skb)
+void __dev_kfree_skb_any(struct sk_buff *skb, enum skb_free_reason reason)
{
if (in_irq() || irqs_disabled())
- dev_kfree_skb_irq(skb);
+ __dev_kfree_skb_irq(skb, reason);
else
dev_kfree_skb(skb);
}
-EXPORT_SYMBOL(dev_kfree_skb_any);
+EXPORT_SYMBOL(__dev_kfree_skb_any);
/**
@@ -3306,7 +3318,10 @@ static void net_tx_action(struct softirq_action *h)
clist = clist->next;
WARN_ON(atomic_read(&skb->users));
- trace_kfree_skb(skb, net_tx_action);
+ if (likely(get_kfree_skb_cb(skb)->reason == SKB_REASON_CONSUMED))
+ trace_consume_skb(skb);
+ else
+ trace_kfree_skb(skb, net_tx_action);
__kfree_skb(skb);
}
}
--
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