From edb09eb17ed89eaa82a52dd306beac93e292b485 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 6 Jun 2016 09:37:16 -0700 Subject: 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 Cc: Cong Wang Cc: Jamal Hadi Salim Cc: John Fastabend Cc: Kevin Athey Cc: Xiaotian Pei Signed-off-by: David S. Miller --- Documentation/networking/gen_stats.txt | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/networking') 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; -- cgit v1.2.1