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authorEric Dumazet <edumazet@google.com>2016-06-06 19:37:16 +0300
committerDavid S. Miller <davem@davemloft.net>2016-06-08 02:37:14 +0300
commitedb09eb17ed89eaa82a52dd306beac93e292b485 (patch)
tree1f241506d6b781b65d1033925f1c1ce6a39c3394 /Documentation/networking
parentf9eb8aea2a1e12fc2f584d1627deeb957435a801 (diff)
downloadlinux-edb09eb17ed89eaa82a52dd306beac93e292b485.tar.xz
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 'Documentation/networking')
-rw-r--r--Documentation/networking/gen_stats.txt2
1 files changed, 1 insertions, 1 deletions
diff --git a/Documentation/networking/gen_stats.txt b/Documentation/networking/gen_stats.txt
index ff630a87b511..179b18ce45ff 100644
--- a/Documentation/networking/gen_stats.txt
+++ b/Documentation/networking/gen_stats.txt
@@ -21,7 +21,7 @@ struct mystruct {
...
};
-Update statistics:
+Update statistics, in dequeue() methods only, (while owning qdisc->running)
mystruct->tstats.packet++;
mystruct->qstats.backlog += skb->pkt_len;