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Date: Tue, 4 Aug 2009 07:22:05 +0000
From: Jarek Poplawski <jarkao2@...il.com>
To: Krishna Kumar2 <krkumar2@...ibm.com>
Cc: davem@...emloft.net, herbert@...dor.apana.org.au, kaber@...sh.net,
netdev@...r.kernel.org
Subject: Re: [RFC] [PATCH] Avoid enqueuing skb for default qdiscs
On Tue, Aug 04, 2009 at 12:25:07PM +0530, Krishna Kumar2 wrote:
> Jarek Poplawski <jarkao2@...il.com> wrote on 08/04/2009 01:08:47 AM:
>
> Hi Jarek,
>
> > Since this quoted part looks very similarly I'm using it here, so
> > forget my note if something has changed.
>
> Thanks for your feedback. Yes, the inline patch is the same as the
> attached one.
>
> > >> @@ -306,6 +312,9 @@ extern struct Qdisc *qdisc_create_dflt(s
> > >> struct Qdisc_ops *ops, u32 parentid);
> > >> extern void qdisc_calculate_pkt_len(struct sk_buff *skb,
> > >> struct qdisc_size_table *stab);
> > >> +extern int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
> > >> + struct net_device *dev, struct netdev_queue *txq,
> > >> + spinlock_t *root_lock);
> >
> > Probably this would look better in pkt_sched.h around __qdisc_run()?
>
> I had it originally in pkt_sched.h, for some reason I had moved it to
> sch_generic.h, I will move it back.
>
> > >> +static inline int __dev_hw_xmit(struct sk_buff *skb, struct Qdisc *q,
> >
> > I guess, we don't touch "hw" in this function yet?
>
> Right - this was due to lack of a good name. Maybe I can call it
> __dev_xmit_skb?
Looks better to me.
>
> > >> - kfree_skb(qdisc->gso_skb);
> > >> - qdisc->gso_skb = NULL;
> > >> + if (qdisc->gso_skb) {
> > >> + kfree_skb(qdisc->gso_skb);
> > >> + qdisc->gso_skb = NULL;
> > >> + qdisc->q.qlen--;
> >
> > You don't need this here: qdiscs should zero it in ops->reset().
>
> I will keep it around, as you said in your other mail.
Actually I meant:
- qdisc->q.qlen--;
+ qdisc->q.qlen = 0;
because you can do it after another qdisc->q.qlen = 0.
>
> > >> + /* Can by-pass the queue discipline for default qdisc */
> > >> + qdisc->flags = TCQ_F_CAN_BYPASS;
> >
> > "|=" looks nicer to me.
>
> Agreed - and required if qdisc_create_dflt (and the functions it calls)
> is changed to set the flags.
>
> > >> } else {
> > >> qdisc = &noqueue_qdisc;
> > >> }
> >
> > I wonder if we shouldn't update bstats yet. Btw, try checkpatch.
>
> Rate estimator isn't used for default qdisc, so is anything
> required?
I meant "Sent" stats from "tc -s qdisc sh" could be misleading.
> Also, checkpatch suggested to change the original code:
> "if (unlikely((skb = dequeue_skb(q)) == NULL))"
> since it appears as "new code", hope that change is fine.
I mainly meant a whitespace warning.
>
> The patch after incorporating the review comments is both attached
> and inlined, since my mailer is still not working (I sent this mail
> about an hour back but this one didn't seem to have made it while
> one of my latter mails did).
I got 2 very similar messages this time, several minutes ago ;-)
Thanks,
Jarek P.
>
> Thanks,
>
> - KK
>
> (See attached file: patch4)
>
> ----------------------------------------------------------------------
> include/net/pkt_sched.h | 3 +
> include/net/sch_generic.h | 6 ++
> net/core/dev.c | 46 ++++++++++++-----
> net/sched/sch_generic.c | 93 ++++++++++++++++++++++--------------
> 4 files changed, 99 insertions(+), 49 deletions(-)
>
> diff -ruNp org/include/net/pkt_sched.h new/include/net/pkt_sched.h
> --- org/include/net/pkt_sched.h 2009-08-04 11:41:21.000000000 +0530
> +++ new/include/net/pkt_sched.h 2009-08-04 11:42:18.000000000 +0530
> @@ -87,6 +87,9 @@ extern struct qdisc_rate_table *qdisc_ge
> extern void qdisc_put_rtab(struct qdisc_rate_table *tab);
> extern void qdisc_put_stab(struct qdisc_size_table *tab);
> extern void qdisc_warn_nonwc(char *txt, struct Qdisc *qdisc);
> +extern int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
> + struct net_device *dev, struct netdev_queue
> *txq,
> + spinlock_t *root_lock);
>
> extern void __qdisc_run(struct Qdisc *q);
>
> diff -ruNp org/include/net/sch_generic.h new/include/net/sch_generic.h
> --- org/include/net/sch_generic.h 2009-03-24 08:54:16.000000000 +0530
> +++ new/include/net/sch_generic.h 2009-08-04 11:02:39.000000000 +0530
> @@ -45,6 +45,7 @@ struct Qdisc
> #define TCQ_F_BUILTIN 1
> #define TCQ_F_THROTTLED 2
> #define TCQ_F_INGRESS 4
> +#define TCQ_F_CAN_BYPASS 8
> #define TCQ_F_WARN_NONWC (1 << 16)
> int padded;
> struct Qdisc_ops *ops;
> @@ -182,6 +183,11 @@ struct qdisc_skb_cb {
> char data[];
> };
>
> +static inline int qdisc_qlen(struct Qdisc *q)
> +{
> + return q->q.qlen;
> +}
> +
> static inline struct qdisc_skb_cb *qdisc_skb_cb(struct sk_buff *skb)
> {
> return (struct qdisc_skb_cb *)skb->cb;
> diff -ruNp org/net/core/dev.c new/net/core/dev.c
> --- org/net/core/dev.c 2009-07-27 09:08:24.000000000 +0530
> +++ new/net/core/dev.c 2009-08-04 11:44:57.000000000 +0530
> @@ -1786,6 +1786,38 @@ static struct netdev_queue *dev_pick_tx(
> return netdev_get_tx_queue(dev, queue_index);
> }
>
> +static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
> + struct net_device *dev,
> + struct netdev_queue *txq)
> +{
> + spinlock_t *root_lock = qdisc_lock(q);
> + int rc;
> +
> + spin_lock(root_lock);
> + if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) {
> + kfree_skb(skb);
> + rc = NET_XMIT_DROP;
> + } else if ((q->flags & TCQ_F_CAN_BYPASS) && !qdisc_qlen(q) &&
> + !test_and_set_bit(__QDISC_STATE_RUNNING, &q->state)) {
> + /*
> + * This is a work-conserving queue; there are no old skbs
> + * waiting to be sent out; and the qdisc is not running -
> + * xmit the skb directly.
> + */
> + if (sch_direct_xmit(skb, q, dev, txq, root_lock))
> + __qdisc_run(q);
> + else
> + clear_bit(__QDISC_STATE_RUNNING, &q->state);
> + rc = NET_XMIT_SUCCESS;
> + } else {
> + rc = qdisc_enqueue_root(skb, q);
> + qdisc_run(q);
> + }
> + spin_unlock(root_lock);
> +
> + return rc;
> +}
> +
> /**
> * dev_queue_xmit - transmit a buffer
> * @skb: buffer to transmit
> @@ -1859,19 +1891,7 @@ gso:
> skb->tc_verd = SET_TC_AT(skb->tc_verd,AT_EGRESS);
> #endif
> if (q->enqueue) {
> - spinlock_t *root_lock = qdisc_lock(q);
> -
> - spin_lock(root_lock);
> -
> - if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED,
> &q->state))) {
> - kfree_skb(skb);
> - rc = NET_XMIT_DROP;
> - } else {
> - rc = qdisc_enqueue_root(skb, q);
> - qdisc_run(q);
> - }
> - spin_unlock(root_lock);
> -
> + rc = __dev_xmit_skb(skb, q, dev, txq);
> goto out;
> }
>
> 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 2009-08-04 11:00:38.000000000 +0530
> @@ -37,15 +37,11 @@
> * - updates to tree and tree walking are only done under the rtnl mutex.
> */
>
> -static inline int qdisc_qlen(struct Qdisc *q)
> -{
> - return q->q.qlen;
> -}
> -
> static inline int dev_requeue_skb(struct sk_buff *skb, struct Qdisc *q)
> {
> q->gso_skb = skb;
> q->qstats.requeues++;
> + q->q.qlen++; /* it's still part of the queue */
> __netif_schedule(q);
>
> return 0;
> @@ -61,9 +57,11 @@ static inline struct sk_buff *dequeue_sk
>
> /* 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_stopped(txq) &&
> + !netif_tx_queue_frozen(txq)) {
> q->gso_skb = NULL;
> - else
> + q->q.qlen--;
> + } else
> skb = NULL;
> } else {
> skb = q->dequeue(q);
> @@ -103,44 +101,23 @@ static inline int handle_dev_cpu_collisi
> }
>
> /*
> - * NOTE: Called under qdisc_lock(q) with locally disabled BH.
> - *
> - * __QDISC_STATE_RUNNING guarantees only one CPU can process
> - * this qdisc at a time. qdisc_lock(q) serializes queue accesses for
> - * this queue.
> - *
> - * netif_tx_lock serializes accesses to device driver.
> - *
> - * qdisc_lock(q) and netif_tx_lock are mutually exclusive,
> - * if one is grabbed, another must be free.
> - *
> - * Note, that this procedure can be called by a watchdog timer
> + * Transmit one skb, and handle the return status as required. Holding the
> + * __QDISC_STATE_RUNNING bit guarantees that only one CPU can execute this
> + * function.
> *
> * Returns to the caller:
> * 0 - queue is empty or throttled.
> * >0 - queue is not empty.
> - *
> */
> -static inline int qdisc_restart(struct Qdisc *q)
> +int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
> + struct net_device *dev, struct netdev_queue *txq,
> + spinlock_t *root_lock)
> {
> - struct netdev_queue *txq;
> int ret = NETDEV_TX_BUSY;
> - struct net_device *dev;
> - spinlock_t *root_lock;
> - struct sk_buff *skb;
> -
> - /* Dequeue packet */
> - if (unlikely((skb = dequeue_skb(q)) == NULL))
> - return 0;
> -
> - root_lock = qdisc_lock(q);
>
> /* And release qdisc */
> spin_unlock(root_lock);
>
> - dev = qdisc_dev(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))
> @@ -177,6 +154,44 @@ static inline int qdisc_restart(struct Q
> return ret;
> }
>
> +/*
> + * NOTE: Called under qdisc_lock(q) with locally disabled BH.
> + *
> + * __QDISC_STATE_RUNNING guarantees only one CPU can process
> + * this qdisc at a time. qdisc_lock(q) serializes queue accesses for
> + * this queue.
> + *
> + * netif_tx_lock serializes accesses to device driver.
> + *
> + * qdisc_lock(q) and netif_tx_lock are mutually exclusive,
> + * if one is grabbed, another must be free.
> + *
> + * Note, that this procedure can be called by a watchdog timer
> + *
> + * Returns to the caller:
> + * 0 - queue is empty or throttled.
> + * >0 - queue is not empty.
> + *
> + */
> +static inline int qdisc_restart(struct Qdisc *q)
> +{
> + struct netdev_queue *txq;
> + struct net_device *dev;
> + spinlock_t *root_lock;
> + struct sk_buff *skb;
> +
> + /* Dequeue packet */
> + skb = dequeue_skb(q);
> + if (unlikely(!skb))
> + return 0;
> +
> + root_lock = qdisc_lock(q);
> + dev = qdisc_dev(q);
> + txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));
> +
> + return sch_direct_xmit(skb, q, dev, txq, root_lock);
> +}
> +
> void __qdisc_run(struct Qdisc *q)
> {
> unsigned long start_time = jiffies;
> @@ -547,8 +562,11 @@ void qdisc_reset(struct Qdisc *qdisc)
> if (ops->reset)
> ops->reset(qdisc);
>
> - kfree_skb(qdisc->gso_skb);
> - qdisc->gso_skb = NULL;
> + if (qdisc->gso_skb) {
> + kfree_skb(qdisc->gso_skb);
> + qdisc->gso_skb = NULL;
> + qdisc->q.qlen--;
> + }
> }
> EXPORT_SYMBOL(qdisc_reset);
>
> @@ -605,6 +623,9 @@ static void attach_one_default_qdisc(str
> printk(KERN_INFO "%s: activation failed\n",
> dev->name);
> return;
> }
> +
> + /* Can by-pass the queue discipline for default qdisc */
> + qdisc->flags |= TCQ_F_CAN_BYPASS;
> } else {
> qdisc = &noqueue_qdisc;
> }
--
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