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net_sched: htb: do not acquire qdisc lock in dump operations 

htb_dump() and htb_dump_class() do not strictly need to acquire
qdisc lock to fetch qdisc and/or class parameters.

We hold RTNL and no changes can occur.

This reduces by 50% qdisc lock pressure while doing tc qdisc|class dump
operations.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2014-03-05 10:14:34 -08:00 committed by David S. Miller
parent e86800f920
commit 6f542efcbc
1 changed files with 8 additions and 12 deletions
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20
net/sched/sch_htb.c
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@ -1062,12 +1062,13 @@ static int htb_init(struct Qdisc *sch, struct nlattr *opt)
static int htb_dump(struct Qdisc *sch, struct sk_buff *skb)
{
spinlock_t *root_lock = qdisc_root_sleeping_lock(sch);
struct htb_sched *q = qdisc_priv(sch);
struct nlattr *nest;
struct tc_htb_glob gopt;
spin_lock_bh(root_lock);
/* Its safe to not acquire qdisc lock. As we hold RTNL,
* no change can happen on the qdisc parameters.
*/
gopt.direct_pkts = q->direct_pkts;
gopt.version = HTB_VER;
@ -1081,13 +1082,10 @@ static int htb_dump(struct Qdisc *sch, struct sk_buff *skb)
if (nla_put(skb, TCA_HTB_INIT, sizeof(gopt), &gopt) ||
nla_put_u32(skb, TCA_HTB_DIRECT_QLEN, q->direct_qlen))
goto nla_put_failure;
nla_nest_end(skb, nest);
spin_unlock_bh(root_lock);
return skb->len;
return nla_nest_end(skb, nest);
nla_put_failure:
spin_unlock_bh(root_lock);
nla_nest_cancel(skb, nest);
return -1;
}
@ -1096,11 +1094,12 @@ static int htb_dump_class(struct Qdisc *sch, unsigned long arg,
struct sk_buff *skb, struct tcmsg *tcm)
{
struct htb_class *cl = (struct htb_class *)arg;
spinlock_t *root_lock = qdisc_root_sleeping_lock(sch);
struct nlattr *nest;
struct tc_htb_opt opt;
spin_lock_bh(root_lock);
/* Its safe to not acquire qdisc lock. As we hold RTNL,
* no change can happen on the class parameters.
*/
tcm->tcm_parent = cl->parent ? cl->parent->common.classid : TC_H_ROOT;
tcm->tcm_handle = cl->common.classid;
if (!cl->level && cl->un.leaf.q)
@ -1128,12 +1127,9 @@ static int htb_dump_class(struct Qdisc *sch, unsigned long arg,
nla_put_u64(skb, TCA_HTB_CEIL64, cl->ceil.rate_bytes_ps))
goto nla_put_failure;
nla_nest_end(skb, nest);
spin_unlock_bh(root_lock);
return skb->len;
return nla_nest_end(skb, nest);
nla_put_failure:
spin_unlock_bh(root_lock);
nla_nest_cancel(skb, nest);
return -1;
}