diff options
| author | Eric Dumazet <edumazet@google.com> | 2016-06-06 09:37:16 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-06-07 16:37:14 -0700 |
| commit | edb09eb17ed89eaa82a52dd306beac93e292b485 (patch) | |
| tree | 1f241506d6b781b65d1033925f1c1ce6a39c3394 /net/sched/sch_mq.c | |
| parent | f9eb8aea2a1e12fc2f584d1627deeb957435a801 (diff) | |
net: sched: do not acquire qdisc spinlock in qdisc/class stats dump
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>
Diffstat (limited to 'net/sched/sch_mq.c')
| -rw-r--r-- | net/sched/sch_mq.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/sched/sch_mq.c b/net/sched/sch_mq.c index 56a77b878eb3..b9439827c172 100644 --- a/net/sched/sch_mq.c +++ b/net/sched/sch_mq.c @@ -199,7 +199,7 @@ static int mq_dump_class_stats(struct Qdisc *sch, unsigned long cl, struct netdev_queue *dev_queue = mq_queue_get(sch, cl); sch = dev_queue->qdisc_sleeping; - if (gnet_stats_copy_basic(d, NULL, &sch->bstats) < 0 || + if (gnet_stats_copy_basic(&sch->running, d, NULL, &sch->bstats) < 0 || gnet_stats_copy_queue(d, NULL, &sch->qstats, sch->q.qlen) < 0) return -1; return 0; |