During Netfilter Workshop 2016 Eric Dumazet pointed out that qdisc
schedulers use doubly-linked lists, even though single-linked list
would be enough.
The double-linked skb lists incur one extra write on enqueue/dequeue
operations (to change ->prev pointer of next list elem).
This series converts qdiscs to single-linked version, listhead
maintains pointers to first (for dequeue) and last skb (for enqueue).
Most qdiscs don't queue at all and instead use a leaf qdisc (typically
pfifo_fast) so only a few schedulers needed changes.
I briefly tested netem and htb and they seemed fine.
UDP_STREAM netperf with 64 byte packets via veth+pfifo_fast shows
a small (~2%) improvement.
Florian Westphal (5):
pie: use qdisc_dequeue_head wrapper
sched: don't use skb queue helpers
sched: remove qdisc arg from __qdisc_dequeue_head
sched: replace __skb_dequeue with __qdisc_dequeue_head
sched: add and use qdisc_skb_head helpers
include/net/sch_generic.h | 72 +++++++++++++++++++++++++++++++++++-----------
net/sched/sch_codel.c | 4 +-
net/sched/sch_fifo.c | 4 +-
net/sched/sch_generic.c | 30 +++++++++++--------
net/sched/sch_htb.c | 24 ++++++++++++---
net/sched/sch_netem.c | 20 +++++++++---
net/sched/sch_pie.c | 4 +-
7 files changed, 115 insertions(+), 43 deletions(-)