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Date: Mon, 20 Jul 2009 13:16:07 +0530
From: Krishna Kumar <krkumar2@...ibm.com>
To: davem@...emloft.net, herbert@...dor.apana.org.au
Cc: netdev@...r.kernel.org, Krishna Kumar <krkumar2@...ibm.com>
Subject: [RFC] [PATCH] Don't run __qdisc_run() on a stopped TX queue
From: Krishna Kumar <krkumar2@...ibm.com>
Driver sends an skb and stops the queue if no more space is
available on the device, and returns OK. When dev_queue_xmit
runs for the next skb, it enqueue's the skb & calls qdisc_run.
qdisc_run dequeue's the skb and finds the queue is stopped
after getting the HARD_LOCK_TX, and puts the skb back on
gso_skb (the next iteration fails faster at dequeue_skb).
This patch avoids calling __qdisc_run if the queue is stopped.
This also lets us remove the queue_stopped check in dequeue_skb
and in qdisc_restart. When the queue is re-enabled, it runs with
one less queue_stopped() check for every skb on the queue (we
still need to own the __QDISC_STATE_RUNNING bit to catch the
stopped condition correctly since stopped cannot be set without
holding this bit).
Results for 3 iteration testing for 1, 4, 8, 12 netperf sessions
running for 1 minute each:
-----------------------------------------------------------------
System-X P6
-----------------------------------------------------------------
Size ORG BW NEW BW ORG BW NEW BW
-----------------------------------------------------------------
16K 72183.05 74417.79 60775.76 63413.17
128K 69097.87 72447.12 61692.16 62251.07
256K 60456.21 61415.81 59694.03 61641.81
-----------------------------------------------------------------
Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
---
include/net/pkt_sched.h | 9 +++++++--
net/sched/sch_generic.c | 9 ++-------
2 files changed, 9 insertions(+), 9 deletions(-)
diff -ruNp org/include/net/pkt_sched.h new/include/net/pkt_sched.h
--- org/include/net/pkt_sched.h 2009-06-22 11:40:31.000000000 +0530
+++ new/include/net/pkt_sched.h 2009-07-20 13:09:18.000000000 +0530
@@ -92,8 +92,13 @@ extern void __qdisc_run(struct Qdisc *q)
static inline void qdisc_run(struct Qdisc *q)
{
- if (!test_and_set_bit(__QDISC_STATE_RUNNING, &q->state))
- __qdisc_run(q);
+ if (!test_and_set_bit(__QDISC_STATE_RUNNING, &q->state)) {
+ if (!netif_tx_queue_stopped(q->dev_queue))
+ __qdisc_run(q);
+ else
+ /* driver will wake us up anyway, just clear */
+ clear_bit(__QDISC_STATE_RUNNING, &q->state);
+ }
}
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 2009-05-25 07:48:07.000000000 +0530
+++ new/net/sched/sch_generic.c 2009-07-20 13:09:18.000000000 +0530
@@ -56,12 +56,8 @@ static inline struct sk_buff *dequeue_sk
struct sk_buff *skb = q->gso_skb;
if (unlikely(skb)) {
- struct net_device *dev = qdisc_dev(q);
- struct netdev_queue *txq;
-
/* check the reason of requeuing without tx lock first */
- txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));
- if (!netif_tx_queue_stopped(txq) && !netif_tx_queue_frozen(txq))
+ if (!netif_tx_queue_frozen(q->dev_queue))
q->gso_skb = NULL;
else
skb = NULL;
@@ -142,8 +138,7 @@ static inline int qdisc_restart(struct Q
txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));
HARD_TX_LOCK(dev, txq, smp_processor_id());
- if (!netif_tx_queue_stopped(txq) &&
- !netif_tx_queue_frozen(txq))
+ if (!netif_tx_queue_frozen(txq))
ret = dev_hard_start_xmit(skb, dev, txq);
HARD_TX_UNLOCK(dev, txq);
--
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