[PATCH 3/9 Rev3] [sched] Modify qdisc_run to support batching

Krishna Kumar
2007-08-08T09:32:45Z

Modify qdisc_run() to support batching. Modify callers of qdisc_run to
use batching, modify qdisc_restart to implement batching.

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
---
include/net/pkt_sched.h | 6 +--
net/core/dev.c | 5 +--
net/sched/sch_generic.c | 77 +++++++++++++++++++++++++++++++++++++++---------
3 files changed, 69 insertions(+), 19 deletions(-)

diff -ruNp ORG/include/net/pkt_sched.h NEW/include/net/pkt_sched.h
--- ORG/include/net/pkt_sched.h 2007-07-17 08:48:37.000000000 +0530
+++ NEW/include/net/pkt_sched.h 2007-08-07 13:11:19.000000000 +0530
@@ -80,13 +80,13 @@ extern struct qdisc_rate_table *qdisc_ge
struct rtattr *tab);
extern void qdisc_put_rtab(struct qdisc_rate_table *tab);

-extern void __qdisc_run(struct net_device *dev);
+extern void __qdisc_run(struct net_device *dev, struct sk_buff_head *blist);

-static inline void qdisc_run(struct net_device *dev)
+static inline void qdisc_run(struct net_device *dev, struct sk_buff_head *blist)
{
if (!netif_queue_stopped(dev) &&
!test_and_set_bit(__LINK_STATE_QDISC_RUNNING, &dev->state))
- __qdisc_run(dev);
+ __qdisc_run(dev, blist);
}

extern int tc_classify_compat(struct sk_buff *skb, struct tcf_proto *tp,
diff -ruNp ORG/net/sched/sch_generic.c NEW/net/sched/sch_generic.c
--- ORG/net/sched/sch_generic.c 2007-07-12 08:55:20.000000000 +0530
+++ NEW/net/sched/sch_generic.c 2007-08-07 13:11:19.000000000 +0530
@@ -59,10 +59,12 @@ static inline int qdisc_qlen(struct Qdis
static inline int dev_requeue_skb(struct sk_buff *skb, struct net_device *dev,
struct Qdisc *q)
{
- if (unlikely(skb->next))
- dev->gso_skb = skb;
- else
- q->ops->requeue(skb, q);
+ if (likely(skb)) {
+ if (unlikely(skb->next))
+ dev->gso_skb = skb;
+ else
+ q->ops->requeue(skb, q);
+ }

netif_schedule(dev);
return 0;
@@ -91,17 +93,22 @@ static inline int handle_dev_cpu_collisi
/*
* Same CPU holding the lock. It may be a transient
* configuration error, when hard_start_xmit() recurses. We
- * detect it by checking xmit owner and drop the packet when
- * deadloop is detected. Return OK to try the next skb.
+ * detect it by checking xmit owner and drop the packet (or
+ * all packets in batching case) when deadloop is detected.
+ * Return OK to try the next skb.
*/
- kfree_skb(skb);
+ if (likely(skb))
+ kfree_skb(skb);
+ else if (!skb_queue_empty(dev->skb_blist))
+ skb_queue_purge(dev->skb_blist);
+
if (net_ratelimit())
printk(KERN_WARNING "Dead loop on netdevice %s, "
"fix it urgently!\n", dev->name);
ret = qdisc_qlen(q);
} else {
/*
- * Another cpu is holding lock, requeue & delay xmits for
+ * Another cpu is holding lock, requeue skb & delay xmits for
* some time.
*/
__get_cpu_var(netdev_rx_stat).cpu_collision++;
@@ -112,6 +119,38 @@ static inline int handle_dev_cpu_collisi
}

/*
+ * Algorithm to get skb(s) is:
+ * - Non batching drivers, or if the batch list is empty and there is
+ * 1 skb in the queue - dequeue skb and put it in *skbp to tell the
+ * caller to use the single xmit API.
+ * - Batching drivers where the batch list already contains atleast one
+ * skb, or if there are multiple skbs in the queue: keep dequeue'ing
+ * skb's upto a limit and set *skbp to NULL to tell the caller to use
+ * the multiple xmit API.
+ *
+ * Returns:
+ * 1 - atleast one skb is to be sent out, *skbp contains skb or NULL
+ * (in case >1 skbs present in blist for batching)
+ * 0 - no skbs to be sent.
+ */
+static inline int get_skb(struct net_device *dev, struct Qdisc *q,
+ struct sk_buff_head *blist, struct sk_buff **skbp)
+{
+ if (likely(!blist || (!skb_queue_len(blist) && qdisc_qlen(q) <= 1))) {
+ return likely((*skbp = dev_dequeue_skb(dev, q)) != NULL);
+ } else {
+ int max = dev->tx_queue_len - skb_queue_len(blist);
+ struct sk_buff *skb;
+
+ while (max > 0 && (skb = dev_dequeue_skb(dev, q)) != NULL)
+ max -= dev_add_skb_to_blist(skb, dev);
+
+ *skbp = NULL;
+ return 1; /* we have atleast one skb in blist */
+ }
+}
+
+/*
* NOTE: Called under dev->queue_lock with locally disabled BH.
*
* __LINK_STATE_QDISC_RUNNING guarantees only one CPU can process this
@@ -130,7 +169,8 @@ static inline int handle_dev_cpu_collisi
* >0 - queue is not empty.
*
*/
-static inline int qdisc_restart(struct net_device *dev)
+static inline int qdisc_restart(struct net_device *dev,
+ struct sk_buff_head *blist)
{
struct Qdisc *q = dev->qdisc;
struct sk_buff *skb;
@@ -138,7 +178,7 @@ static inline int qdisc_restart(struct n
int ret;

/* Dequeue packet */
- if (unlikely((skb = dev_dequeue_skb(dev, q)) == NULL))
+ if (unlikely(!get_skb(dev, q, blist, &skb)))
return 0;

/*
@@ -158,7 +198,10 @@ static inline int qdisc_restart(struct n
/* And release queue */
spin_unlock(&dev->queue_lock);

- ret = dev_hard_start_xmit(skb, dev);
+ if (likely(skb))
+ ret = dev_hard_start_xmit(skb, dev);
+ else
+ ret = dev->hard_start_xmit_batch(dev);

if (!lockless)
netif_tx_unlock(dev);
@@ -168,7 +211,7 @@ static inline int qdisc_restart(struct n

switch (ret) {
case NETDEV_TX_OK:
- /* Driver sent out skb successfully */
+ /* Driver sent out skb (or entire skb_blist) successfully */
ret = qdisc_qlen(q);
break;

@@ -190,10 +233,10 @@ static inline int qdisc_restart(struct n
return ret;
}

-void __qdisc_run(struct net_device *dev)
+void __qdisc_run(struct net_device *dev, struct sk_buff_head *blist)
{
do {
- if (!qdisc_restart(dev))
+ if (!qdisc_restart(dev, blist))
break;
} while (!netif_queue_stopped(dev));

@@ -563,6 +606,12 @@ void dev_deactivate(struct net_device *d
qdisc = dev->qdisc;
dev->qdisc = &noop_qdisc;

+ if (dev->skb_blist) {
+ /* Release skbs on batch list */
+ if (!skb_queue_empty(dev->skb_blist))
+ skb_queue_purge(dev->skb_blist);
+ }
+
qdisc_reset(qdisc);

skb = dev->gso_skb;
diff -ruNp ORG/net/core/dev.c NEW/net/core/dev.c
--- ORG/net/core/dev.c 2007-08-06 08:25:40.000000000 +0530
+++ NEW/net/core/dev.c 2007-08-07 13:11:19.000000000 +0530
@@ -1699,7 +1699,7 @@ gso:
/* reset queue_mapping to zero */
skb->queue_mapping = 0;
rc = q->enqueue(skb, q);
- qdisc_run(dev);
+ qdisc_run(dev, NULL);
spin_unlock(&dev->queue_lock);

rc = rc == NET_XMIT_BYPASS ? NET_XMIT_SUCCESS : rc;
@@ -1896,7 +1896,8 @@ static void net_tx_action(struct softirq
clear_bit(__LINK_STATE_SCHED, &dev->state);

if (spin_trylock(&dev->queue_lock)) {
- qdisc_run(dev);
+ /* Send all skbs if driver supports batching */
+ qdisc_run(dev, dev->skb_blist);
spin_unlock(&dev->queue_lock);
} else {
netif_schedule(dev);