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net_sched: RCU conversion of stab

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This patch converts stab qdisc management to RCU, so that we can perform
the qdisc_calculate_pkt_len() call before getting qdisc lock.

This shortens the lock's held time in __dev_xmit_skb().

This permits more qdiscs to get TCQ_F_CAN_BYPASS status, avoiding lot of
cache misses and so reducing latencies.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Jesper Dangaard Brouer <hawk@diku.dk>
CC: Jarek Poplawski <jarkao2@gmail.com>
CC: Jamal Hadi Salim <hadi@cyberus.ca>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2011-01-20 03:48:19 +00:00
committed by David S. Miller
parent fd245a4adb
commit a2da570d62
4 changed files with 38 additions and 19 deletions
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26
net/sched/sch_api.c
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@@ -398,6 +398,11 @@ static struct qdisc_size_table *qdisc_get_stab(struct nlattr *opt)
return stab;
}
static void stab_kfree_rcu(struct rcu_head *head)
{
kfree(container_of(head, struct qdisc_size_table, rcu));
}
void qdisc_put_stab(struct qdisc_size_table *tab)
{
if (!tab)
@@ -407,7 +412,7 @@ void qdisc_put_stab(struct qdisc_size_table *tab)
if (--tab->refcnt == 0) {
list_del(&tab->list);
kfree(tab);
call_rcu_bh(&tab->rcu, stab_kfree_rcu);
}
spin_unlock(&qdisc_stab_lock);
@@ -430,7 +435,7 @@ nla_put_failure:
return -1;
}
void qdisc_calculate_pkt_len(struct sk_buff *skb, struct qdisc_size_table *stab)
void __qdisc_calculate_pkt_len(struct sk_buff *skb, const struct qdisc_size_table *stab)
{
int pkt_len, slot;
@@ -456,7 +461,7 @@ out:
pkt_len = 1;
qdisc_skb_cb(skb)->pkt_len = pkt_len;
}
EXPORT_SYMBOL(qdisc_calculate_pkt_len);
EXPORT_SYMBOL(__qdisc_calculate_pkt_len);
void qdisc_warn_nonwc(char *txt, struct Qdisc *qdisc)
{
@@ -835,7 +840,7 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
err = PTR_ERR(stab);
goto err_out4;
}
sch->stab = stab;
rcu_assign_pointer(sch->stab, stab);
}
if (tca[TCA_RATE]) {
spinlock_t *root_lock;
@@ -875,7 +880,7 @@ err_out4:
* Any broken qdiscs that would require a ops->reset() here?
* The qdisc was never in action so it shouldn't be necessary.
*/
qdisc_put_stab(sch->stab);
qdisc_put_stab(rtnl_dereference(sch->stab));
if (ops->destroy)
ops->destroy(sch);
goto err_out3;
@@ -883,7 +888,7 @@ err_out4:
static int qdisc_change(struct Qdisc *sch, struct nlattr **tca)
{
struct qdisc_size_table *stab = NULL;
struct qdisc_size_table *ostab, *stab = NULL;
int err = 0;
if (tca[TCA_OPTIONS]) {
@@ -900,8 +905,9 @@ static int qdisc_change(struct Qdisc *sch, struct nlattr **tca)
return PTR_ERR(stab);
}
qdisc_put_stab(sch->stab);
sch->stab = stab;
ostab = rtnl_dereference(sch->stab);
rcu_assign_pointer(sch->stab, stab);
qdisc_put_stab(ostab);
if (tca[TCA_RATE]) {
/* NB: ignores errors from replace_estimator
@@ -1180,6 +1186,7 @@ static int tc_fill_qdisc(struct sk_buff *skb, struct Qdisc *q, u32 clid,
struct nlmsghdr *nlh;
unsigned char *b = skb_tail_pointer(skb);
struct gnet_dump d;
struct qdisc_size_table *stab;
nlh = NLMSG_NEW(skb, pid, seq, event, sizeof(*tcm), flags);
tcm = NLMSG_DATA(nlh);
@@ -1195,7 +1202,8 @@ static int tc_fill_qdisc(struct sk_buff *skb, struct Qdisc *q, u32 clid,
goto nla_put_failure;
q->qstats.qlen = q->q.qlen;
if (q->stab && qdisc_dump_stab(skb, q->stab) < 0)
stab = rtnl_dereference(q->stab);
if (stab && qdisc_dump_stab(skb, stab) < 0)
goto nla_put_failure;
if (gnet_stats_start_copy_compat(skb, TCA_STATS2, TCA_STATS, TCA_XSTATS,