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Date: Fri, 24 Jul 2009 08:30:06 +0000 From: Jarek Poplawski <jarkao2@...il.com> To: Krishna Kumar <krkumar2@...ibm.com> Cc: davem@...emloft.net, herbert@...dor.apana.org.au, netdev@...r.kernel.org Subject: Re: [RFC] [PATCH] Don't run __qdisc_run() on a stopped TX queue On 20-07-2009 09:46, Krishna Kumar wrote: > 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. It was designed wrt. multiqueue handling mainly, were such a check isn't enough at this place. Jarek P. > 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); > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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