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Date: Thu, 22 Apr 2010 17:09:17 +0800
From: Changli Gao <xiaosuo@...il.com>
To: "David S. Miller" <davem@...emloft.net>
Cc: jamal <hadi@...erus.ca>, Tom Herbert <therbert@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
Changli Gao <xiaosuo@...il.com>
Subject: [PATCH v5] net: batch skb dequeueing from softnet input_pkt_queue
batch skb dequeueing from softnet input_pkt_queue
batch skb dequeueing from softnet input_pkt_queue to reduce potential lock
contention when RPS is enabled. input_pkt_queue is reimplemented as a single
linked list (FIFO) to keep enqueueing and dequeueing as fast as posible, and
input_pkt_queue_lock is moved into RPS section to reduce 4 bytes on 32bits
machine.
Note: input_pkt_queue_len doesn't been decreased until process_backlog()
returns.
Signed-off-by: Changli Gao <xiaosuo@...il.com>
----
include/linux/netdevice.h | 12 ++++-
net/core/dev.c | 99 +++++++++++++++++++++++++++++++++-------------
2 files changed, 82 insertions(+), 29 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3c5ed5f..58abdd5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1387,6 +1387,7 @@ struct softnet_data {
struct Qdisc *output_queue;
struct list_head poll_list;
struct sk_buff *completion_queue;
+ struct sk_buff *process_queue;
#ifdef CONFIG_RPS
struct softnet_data *rps_ipi_list;
@@ -1396,15 +1397,20 @@ struct softnet_data {
struct softnet_data *rps_ipi_next;
unsigned int cpu;
unsigned int input_queue_head;
+ spinlock_t input_pkt_queue_lock;
#endif
- struct sk_buff_head input_pkt_queue;
+ unsigned int input_pkt_queue_len;
+ struct sk_buff *input_pkt_queue_head;
+ struct sk_buff **input_pkt_queue_tailp;
+
struct napi_struct backlog;
};
-static inline void input_queue_head_incr(struct softnet_data *sd)
+static inline void input_queue_head_add(struct softnet_data *sd,
+ unsigned int len)
{
#ifdef CONFIG_RPS
- sd->input_queue_head++;
+ sd->input_queue_head += len;
#endif
}
diff --git a/net/core/dev.c b/net/core/dev.c
index e904c47..f37c223 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -211,14 +211,14 @@ static inline struct hlist_head *dev_index_hash(struct net *net, int ifindex)
static inline void rps_lock(struct softnet_data *sd)
{
#ifdef CONFIG_RPS
- spin_lock(&sd->input_pkt_queue.lock);
+ spin_lock(&sd->input_pkt_queue_lock);
#endif
}
static inline void rps_unlock(struct softnet_data *sd)
{
#ifdef CONFIG_RPS
- spin_unlock(&sd->input_pkt_queue.lock);
+ spin_unlock(&sd->input_pkt_queue_lock);
#endif
}
@@ -2409,12 +2409,15 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
__get_cpu_var(netdev_rx_stat).total++;
rps_lock(sd);
- if (sd->input_pkt_queue.qlen <= netdev_max_backlog) {
- if (sd->input_pkt_queue.qlen) {
+ if (sd->input_pkt_queue_len <= netdev_max_backlog) {
+ if (sd->input_pkt_queue_len) {
enqueue:
- __skb_queue_tail(&sd->input_pkt_queue, skb);
+ skb->next = NULL;
+ *sd->input_pkt_queue_tailp = skb;
+ sd->input_pkt_queue_tailp = &skb->next;
+ sd->input_pkt_queue_len++;
#ifdef CONFIG_RPS
- *qtail = sd->input_queue_head + sd->input_pkt_queue.qlen;
+ *qtail = sd->input_queue_head + sd->input_pkt_queue_len;
#endif
rps_unlock(sd);
local_irq_restore(flags);
@@ -2927,19 +2930,37 @@ EXPORT_SYMBOL(netif_receive_skb);
/* Network device is going away, flush any packets still pending
* Called with irqs disabled.
*/
-static void flush_backlog(void *arg)
+
+static struct sk_buff **__flush_backlog(struct softnet_data *sd,
+ struct sk_buff **pskb,
+ struct net_device *dev)
{
- struct net_device *dev = arg;
- struct softnet_data *sd = &__get_cpu_var(softnet_data);
- struct sk_buff *skb, *tmp;
+ struct sk_buff *skb;
- rps_lock(sd);
- skb_queue_walk_safe(&sd->input_pkt_queue, skb, tmp)
+ while (*pskb) {
+ skb = *pskb;
if (skb->dev == dev) {
- __skb_unlink(skb, &sd->input_pkt_queue);
+ *pskb = skb->next;
kfree_skb(skb);
- input_queue_head_incr(sd);
+ input_queue_head_add(sd, 1);
+ sd->input_pkt_queue_len--;
+ } else {
+ pskb = &skb->next;
}
+ }
+
+ return pskb;
+}
+
+static void flush_backlog(void *arg)
+{
+ struct softnet_data *sd = &__get_cpu_var(softnet_data);
+ struct sk_buff **tailp;
+
+ rps_lock(sd);
+ tailp = __flush_backlog(sd, &sd->input_pkt_queue_head, arg);
+ sd->input_pkt_queue_tailp = tailp;
+ __flush_backlog(sd, &sd->process_queue, arg);
rps_unlock(sd);
}
@@ -3249,24 +3270,39 @@ static int process_backlog(struct napi_struct *napi, int quota)
struct softnet_data *sd = &__get_cpu_var(softnet_data);
napi->weight = weight_p;
+ local_irq_disable();
do {
struct sk_buff *skb;
- local_irq_disable();
+ while (sd->process_queue) {
+ skb = sd->process_queue;
+ sd->process_queue = skb->next;
+ local_irq_enable();
+ __netif_receive_skb(skb);
+ if (++work >= quota) {
+ local_irq_disable();
+ rps_lock(sd);
+ goto out;
+ }
+ local_irq_disable();
+ }
+
rps_lock(sd);
- skb = __skb_dequeue(&sd->input_pkt_queue);
- if (!skb) {
+ if (sd->input_pkt_queue_head == NULL) {
__napi_complete(napi);
- rps_unlock(sd);
- local_irq_enable();
break;
}
- input_queue_head_incr(sd);
+ sd->process_queue = sd->input_pkt_queue_head;
+ sd->input_pkt_queue_head = NULL;
+ sd->input_pkt_queue_tailp = &sd->input_pkt_queue_head;
rps_unlock(sd);
- local_irq_enable();
+ } while (1);
- __netif_receive_skb(skb);
- } while (++work < quota);
+out:
+ sd->input_pkt_queue_len -= work;
+ input_queue_head_add(sd, work);
+ rps_unlock(sd);
+ local_irq_enable();
return work;
}
@@ -5621,10 +5657,17 @@ static int dev_cpu_callback(struct notifier_block *nfb,
local_irq_enable();
/* Process offline CPU's input_pkt_queue */
- while ((skb = __skb_dequeue(&oldsd->input_pkt_queue))) {
+ while ((skb = oldsd->input_pkt_queue_head)) {
+ oldsd->input_pkt_queue_head = skb->next;
+ netif_rx(skb);
+ }
+ while ((skb = oldsd->process_queue)) {
+ oldsd->process_queue = skb->next;
netif_rx(skb);
- input_queue_head_incr(oldsd);
}
+ oldsd->input_pkt_queue_tailp = &oldsd->input_pkt_queue_head;
+ input_queue_head_add(oldsd, oldsd->input_pkt_queue_len);
+ oldsd->input_pkt_queue_len = 0;
return NOTIFY_OK;
}
@@ -5842,11 +5885,15 @@ static int __init net_dev_init(void)
for_each_possible_cpu(i) {
struct softnet_data *sd = &per_cpu(softnet_data, i);
- skb_queue_head_init(&sd->input_pkt_queue);
+ sd->input_pkt_queue_head = NULL;
+ sd->input_pkt_queue_tailp = &sd->input_pkt_queue_head;
+ sd->input_pkt_queue_len = 0;
+ sd->process_queue = NULL;
sd->completion_queue = NULL;
INIT_LIST_HEAD(&sd->poll_list);
#ifdef CONFIG_RPS
+ spin_lock_init(&sd->input_pkt_queue_lock);
sd->csd.func = rps_trigger_softirq;
sd->csd.info = sd;
sd->csd.flags = 0;
--
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