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![Ahmed S. Darwish](/assets/img/avatar_default.png)
The Qdisc::running sequence counter has two uses: 1. Reliably reading qdisc's tc statistics while the qdisc is running (a seqcount read/retry loop at gnet_stats_add_basic()). 2. As a flag, indicating whether the qdisc in question is running (without any retry loops). For the first usage, the Qdisc::running sequence counter write section, qdisc_run_begin() => qdisc_run_end(), covers a much wider area than what is actually needed: the raw qdisc's bstats update. A u64_stats sync point was thus introduced (in previous commits) inside the bstats structure itself. A local u64_stats write section is then started and stopped for the bstats updates. Use that u64_stats sync point mechanism for the bstats read/retry loop at gnet_stats_add_basic(). For the second qdisc->running usage, a __QDISC_STATE_RUNNING bit flag, accessed with atomic bitops, is sufficient. Using a bit flag instead of a sequence counter at qdisc_run_begin/end() and qdisc_is_running() leads to the SMP barriers implicitly added through raw_read_seqcount() and write_seqcount_begin/end() getting removed. All call sites have been surveyed though, and no required ordering was identified. Now that the qdisc->running sequence counter is no longer used, remove it. Note, using u64_stats implies no sequence counter protection for 64-bit architectures. This can lead to the qdisc tc statistics "packets" vs. "bytes" values getting out of sync on rare occasions. The individual values will still be valid. Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: David S. Miller <davem@davemloft.net>
278 lines
6.7 KiB
C
278 lines
6.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* net/sched/sch_mq.c Classful multiqueue dummy scheduler
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*
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* Copyright (c) 2009 Patrick McHardy <kaber@trash.net>
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*/
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#include <linux/types.h>
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#include <linux/slab.h>
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/string.h>
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#include <linux/errno.h>
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#include <linux/skbuff.h>
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#include <net/netlink.h>
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#include <net/pkt_cls.h>
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#include <net/pkt_sched.h>
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#include <net/sch_generic.h>
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struct mq_sched {
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struct Qdisc **qdiscs;
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};
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static int mq_offload(struct Qdisc *sch, enum tc_mq_command cmd)
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{
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struct net_device *dev = qdisc_dev(sch);
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struct tc_mq_qopt_offload opt = {
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.command = cmd,
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.handle = sch->handle,
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};
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if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
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return -EOPNOTSUPP;
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return dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_MQ, &opt);
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}
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static int mq_offload_stats(struct Qdisc *sch)
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{
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struct tc_mq_qopt_offload opt = {
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.command = TC_MQ_STATS,
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.handle = sch->handle,
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.stats = {
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.bstats = &sch->bstats,
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.qstats = &sch->qstats,
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},
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};
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return qdisc_offload_dump_helper(sch, TC_SETUP_QDISC_MQ, &opt);
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}
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static void mq_destroy(struct Qdisc *sch)
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{
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struct net_device *dev = qdisc_dev(sch);
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struct mq_sched *priv = qdisc_priv(sch);
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unsigned int ntx;
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mq_offload(sch, TC_MQ_DESTROY);
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if (!priv->qdiscs)
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return;
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for (ntx = 0; ntx < dev->num_tx_queues && priv->qdiscs[ntx]; ntx++)
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qdisc_put(priv->qdiscs[ntx]);
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kfree(priv->qdiscs);
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}
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static int mq_init(struct Qdisc *sch, struct nlattr *opt,
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struct netlink_ext_ack *extack)
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{
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struct net_device *dev = qdisc_dev(sch);
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struct mq_sched *priv = qdisc_priv(sch);
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struct netdev_queue *dev_queue;
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struct Qdisc *qdisc;
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unsigned int ntx;
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if (sch->parent != TC_H_ROOT)
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return -EOPNOTSUPP;
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if (!netif_is_multiqueue(dev))
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return -EOPNOTSUPP;
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/* pre-allocate qdiscs, attachment can't fail */
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priv->qdiscs = kcalloc(dev->num_tx_queues, sizeof(priv->qdiscs[0]),
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GFP_KERNEL);
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if (!priv->qdiscs)
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return -ENOMEM;
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for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
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dev_queue = netdev_get_tx_queue(dev, ntx);
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qdisc = qdisc_create_dflt(dev_queue, get_default_qdisc_ops(dev, ntx),
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TC_H_MAKE(TC_H_MAJ(sch->handle),
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TC_H_MIN(ntx + 1)),
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extack);
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if (!qdisc)
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return -ENOMEM;
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priv->qdiscs[ntx] = qdisc;
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qdisc->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;
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}
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sch->flags |= TCQ_F_MQROOT;
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mq_offload(sch, TC_MQ_CREATE);
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return 0;
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}
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static void mq_attach(struct Qdisc *sch)
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{
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struct net_device *dev = qdisc_dev(sch);
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struct mq_sched *priv = qdisc_priv(sch);
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struct Qdisc *qdisc, *old;
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unsigned int ntx;
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for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
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qdisc = priv->qdiscs[ntx];
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old = dev_graft_qdisc(qdisc->dev_queue, qdisc);
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if (old)
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qdisc_put(old);
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#ifdef CONFIG_NET_SCHED
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if (ntx < dev->real_num_tx_queues)
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qdisc_hash_add(qdisc, false);
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#endif
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}
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kfree(priv->qdiscs);
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priv->qdiscs = NULL;
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}
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static int mq_dump(struct Qdisc *sch, struct sk_buff *skb)
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{
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struct net_device *dev = qdisc_dev(sch);
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struct Qdisc *qdisc;
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unsigned int ntx;
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sch->q.qlen = 0;
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gnet_stats_basic_sync_init(&sch->bstats);
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memset(&sch->qstats, 0, sizeof(sch->qstats));
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/* MQ supports lockless qdiscs. However, statistics accounting needs
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* to account for all, none, or a mix of locked and unlocked child
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* qdiscs. Percpu stats are added to counters in-band and locking
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* qdisc totals are added at end.
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*/
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for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
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qdisc = netdev_get_tx_queue(dev, ntx)->qdisc_sleeping;
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spin_lock_bh(qdisc_lock(qdisc));
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gnet_stats_add_basic(&sch->bstats, qdisc->cpu_bstats,
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&qdisc->bstats, false);
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gnet_stats_add_queue(&sch->qstats, qdisc->cpu_qstats,
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&qdisc->qstats);
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sch->q.qlen += qdisc_qlen(qdisc);
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spin_unlock_bh(qdisc_lock(qdisc));
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}
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return mq_offload_stats(sch);
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}
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static struct netdev_queue *mq_queue_get(struct Qdisc *sch, unsigned long cl)
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{
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struct net_device *dev = qdisc_dev(sch);
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unsigned long ntx = cl - 1;
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if (ntx >= dev->num_tx_queues)
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return NULL;
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return netdev_get_tx_queue(dev, ntx);
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}
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static struct netdev_queue *mq_select_queue(struct Qdisc *sch,
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struct tcmsg *tcm)
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{
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return mq_queue_get(sch, TC_H_MIN(tcm->tcm_parent));
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}
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static int mq_graft(struct Qdisc *sch, unsigned long cl, struct Qdisc *new,
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struct Qdisc **old, struct netlink_ext_ack *extack)
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{
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struct netdev_queue *dev_queue = mq_queue_get(sch, cl);
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struct tc_mq_qopt_offload graft_offload;
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struct net_device *dev = qdisc_dev(sch);
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if (dev->flags & IFF_UP)
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dev_deactivate(dev);
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*old = dev_graft_qdisc(dev_queue, new);
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if (new)
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new->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;
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if (dev->flags & IFF_UP)
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dev_activate(dev);
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graft_offload.handle = sch->handle;
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graft_offload.graft_params.queue = cl - 1;
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graft_offload.graft_params.child_handle = new ? new->handle : 0;
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graft_offload.command = TC_MQ_GRAFT;
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qdisc_offload_graft_helper(qdisc_dev(sch), sch, new, *old,
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TC_SETUP_QDISC_MQ, &graft_offload, extack);
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return 0;
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}
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static struct Qdisc *mq_leaf(struct Qdisc *sch, unsigned long cl)
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{
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struct netdev_queue *dev_queue = mq_queue_get(sch, cl);
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return dev_queue->qdisc_sleeping;
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}
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static unsigned long mq_find(struct Qdisc *sch, u32 classid)
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{
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unsigned int ntx = TC_H_MIN(classid);
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if (!mq_queue_get(sch, ntx))
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return 0;
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return ntx;
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}
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static int mq_dump_class(struct Qdisc *sch, unsigned long cl,
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struct sk_buff *skb, struct tcmsg *tcm)
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{
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struct netdev_queue *dev_queue = mq_queue_get(sch, cl);
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tcm->tcm_parent = TC_H_ROOT;
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tcm->tcm_handle |= TC_H_MIN(cl);
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tcm->tcm_info = dev_queue->qdisc_sleeping->handle;
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return 0;
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}
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static int mq_dump_class_stats(struct Qdisc *sch, unsigned long cl,
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struct gnet_dump *d)
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{
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struct netdev_queue *dev_queue = mq_queue_get(sch, cl);
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sch = dev_queue->qdisc_sleeping;
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if (gnet_stats_copy_basic(d, sch->cpu_bstats, &sch->bstats, true) < 0 ||
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qdisc_qstats_copy(d, sch) < 0)
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return -1;
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return 0;
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}
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static void mq_walk(struct Qdisc *sch, struct qdisc_walker *arg)
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{
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struct net_device *dev = qdisc_dev(sch);
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unsigned int ntx;
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if (arg->stop)
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return;
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arg->count = arg->skip;
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for (ntx = arg->skip; ntx < dev->num_tx_queues; ntx++) {
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if (arg->fn(sch, ntx + 1, arg) < 0) {
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arg->stop = 1;
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break;
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}
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arg->count++;
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}
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}
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static const struct Qdisc_class_ops mq_class_ops = {
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.select_queue = mq_select_queue,
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.graft = mq_graft,
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.leaf = mq_leaf,
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.find = mq_find,
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.walk = mq_walk,
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.dump = mq_dump_class,
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.dump_stats = mq_dump_class_stats,
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};
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struct Qdisc_ops mq_qdisc_ops __read_mostly = {
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.cl_ops = &mq_class_ops,
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.id = "mq",
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.priv_size = sizeof(struct mq_sched),
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.init = mq_init,
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.destroy = mq_destroy,
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.attach = mq_attach,
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.change_real_num_tx = mq_change_real_num_tx,
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.dump = mq_dump,
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.owner = THIS_MODULE,
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};
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