![Eric Dumazet](/assets/img/avatar_default.png)
Large tc dumps (tc -s {qdisc|class} sh dev ethX) done by Google BwE host agent [1] are problematic at scale : For each qdisc/class found in the dump, we currently lock the root qdisc spinlock in order to get stats. Sampling stats every 5 seconds from thousands of HTB classes is a challenge when the root qdisc spinlock is under high pressure. Not only the dumps take time, they also slow down the fast path (queue/dequeue packets) by 10 % to 20 % in some cases. An audit of existing qdiscs showed that sch_fq_codel is the only qdisc that might need the qdisc lock in fq_codel_dump_stats() and fq_codel_dump_class_stats() In v2 of this patch, I now use the Qdisc running seqcount to provide consistent reads of packets/bytes counters, regardless of 32/64 bit arches. I also changed rate estimators to use the same infrastructure so that they no longer need to lock root qdisc lock. [1] http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/43838.pdf Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Cong Wang <xiyou.wangcong@gmail.com> Cc: Jamal Hadi Salim <jhs@mojatatu.com> Cc: John Fastabend <john.fastabend@gmail.com> Cc: Kevin Athey <kda@google.com> Cc: Xiaotian Pei <xiaotian@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
247 lines
5.8 KiB
C
247 lines
5.8 KiB
C
/*
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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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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* version 2 as published by the Free Software Foundation.
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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_sched.h>
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struct mq_sched {
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struct Qdisc **qdiscs;
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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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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_destroy(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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{
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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 == NULL)
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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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if (qdisc == NULL)
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goto err;
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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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return 0;
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err:
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mq_destroy(sch);
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return -ENOMEM;
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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_destroy(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_list_add(qdisc);
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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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memset(&sch->bstats, 0, sizeof(sch->bstats));
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memset(&sch->qstats, 0, sizeof(sch->qstats));
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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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sch->q.qlen += qdisc->q.qlen;
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sch->bstats.bytes += qdisc->bstats.bytes;
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sch->bstats.packets += qdisc->bstats.packets;
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sch->qstats.backlog += qdisc->qstats.backlog;
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sch->qstats.drops += qdisc->qstats.drops;
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sch->qstats.requeues += qdisc->qstats.requeues;
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sch->qstats.overlimits += qdisc->qstats.overlimits;
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spin_unlock_bh(qdisc_lock(qdisc));
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}
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return 0;
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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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unsigned int ntx = TC_H_MIN(tcm->tcm_parent);
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struct netdev_queue *dev_queue = mq_queue_get(sch, ntx);
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if (!dev_queue) {
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struct net_device *dev = qdisc_dev(sch);
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return netdev_get_tx_queue(dev, 0);
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}
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return dev_queue;
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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)
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{
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struct netdev_queue *dev_queue = mq_queue_get(sch, cl);
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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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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_get(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 void mq_put(struct Qdisc *sch, unsigned long cl)
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{
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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(&sch->running, d, NULL, &sch->bstats) < 0 ||
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gnet_stats_copy_queue(d, NULL, &sch->qstats, sch->q.qlen) < 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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.get = mq_get,
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.put = mq_put,
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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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.dump = mq_dump,
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.owner = THIS_MODULE,
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};
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