netdev - [PATCH net-next v3 0/2] net/sched: remove spinlock from 'csum' action

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Date:   Mon, 22 Jan 2018 18:14:30 +0100
From:   Davide Caratti <dcaratti@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     Jiri Pirko <jiri@...nulli.us>
Subject: [PATCH net-next v3 0/2] net/sched: remove spinlock from 'csum' action

Similarly to what has been done earlier with other actions [1][2], this
series tries to improve the performance of 'csum' tc action, removing a
spinlock in the data path. Patch 1 lets act_csum use per-CPU counters;
patch 2 removes spin_{,un}lock_bh() calls from the act() method.

test procedure (using pktgen from https://github.com/netoptimizer):

 # ip link add name eth1 type dummy
 # ip link set dev eth1 up
 # tc qdisc add dev eth1 root handle 1: prio
 # for a in pass drop; do
 > tc filter del dev eth1 parent 1: pref 10 matchall action csum udp
 > tc filter add dev eth1 parent 1: pref 10 matchall action csum udp $a
 > for n in 2 4; do
 > ./pktgen_bench_xmit_mode_queue_xmit.sh -v -s 64 -t $n -n 1000000 -i eth1
 > done
 > done

test results:

      |    |  before patch   |   after patch
  $a  | $n | avg. pps/thread | avg. pps/thread
 -----+----+-----------------+----------------
 pass |  2 |    1671463 ± 4% |    1920789 ± 3%
 pass |  4 |     648797 ± 1% |     738190 ± 1%
 drop |  2 |    3212692 ± 2% |    3719811 ± 2%
 drop |  4 |    1078824 ± 1% |    1328099 ± 1%

references:

[1] https://www.spinics.net/lists/netdev/msg334760.html
[2] https://www.spinics.net/lists/netdev/msg465862.html

v3 changes:
 - use rtnl_dereference() in place of rcu_dereference() in tcf_csum_dump()

v2 changes:
 - add 'drop' test, it produces more contentions
 - use RCU-protected struct to store 'action' and 'update_flags', to avoid
   reading the values from subsequent configurations

Davide Caratti (2):
  net/sched: act_csum: use per-core statistics
  net/sched: act_csum: don't use spinlock in the fast path

 include/net/tc_act/tc_csum.h | 16 +++++++++--
 net/sched/act_csum.c         | 66 ++++++++++++++++++++++++++++++++------------
 2 files changed, 62 insertions(+), 20 deletions(-)

-- 
2.14.3