This is a note to let you know that I've just added the patch titled
net_sched: get rid of rcu_barrier() in tcf_block_put_ext()
to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: net_sched-get-rid-of-rcu_barrier-in-tcf_block_put_ext.patch and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Wed Feb 7 11:29:33 PST 2018
From: Cong Wang xiyou.wangcong@gmail.com Date: Mon, 4 Dec 2017 10:48:18 -0800 Subject: net_sched: get rid of rcu_barrier() in tcf_block_put_ext()
From: Cong Wang xiyou.wangcong@gmail.com
[ Upstream commit efbf78973978b0d25af59bc26c8013a942af6e64 ]
Both Eric and Paolo noticed the rcu_barrier() we use in tcf_block_put_ext() could be a performance bottleneck when we have a lot of tc classes.
Paolo provided the following to demonstrate the issue:
tc qdisc add dev lo root htb for I in `seq 1 1000`; do tc class add dev lo parent 1: classid 1:$I htb rate 100kbit tc qdisc add dev lo parent 1:$I handle $((I + 1)): htb for J in `seq 1 10`; do tc filter add dev lo parent $((I + 1)): u32 match ip src 1.1.1.$J done done time tc qdisc del dev root
real 0m54.764s user 0m0.023s sys 0m0.000s
The rcu_barrier() there is to ensure we free the block after all chains are gone, that is, to queue tcf_block_put_final() at the tail of workqueue. We can achieve this ordering requirement by refcnt'ing tcf block instead, that is, the tcf block is freed only when the last chain in this block is gone. This also simplifies the code.
Paolo reported after this patch we get:
real 0m0.017s user 0m0.000s sys 0m0.017s
Tested-by: Paolo Abeni pabeni@redhat.com Cc: Eric Dumazet edumazet@google.com Cc: Jiri Pirko jiri@mellanox.com Cc: Jamal Hadi Salim jhs@mojatatu.com Signed-off-by: Cong Wang xiyou.wangcong@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/sch_generic.h | 1 - net/sched/cls_api.c | 30 +++++++++--------------------- 2 files changed, 9 insertions(+), 22 deletions(-)
--- a/include/net/sch_generic.h +++ b/include/net/sch_generic.h @@ -280,7 +280,6 @@ struct tcf_block { struct net *net; struct Qdisc *q; struct list_head cb_list; - struct work_struct work; };
static inline void qdisc_cb_private_validate(const struct sk_buff *skb, int sz) --- a/net/sched/cls_api.c +++ b/net/sched/cls_api.c @@ -217,8 +217,12 @@ static void tcf_chain_flush(struct tcf_c
static void tcf_chain_destroy(struct tcf_chain *chain) { + struct tcf_block *block = chain->block; + list_del(&chain->list); kfree(chain); + if (list_empty(&block->chain_list)) + kfree(block); }
static void tcf_chain_hold(struct tcf_chain *chain) @@ -329,27 +333,13 @@ int tcf_block_get(struct tcf_block **p_b } EXPORT_SYMBOL(tcf_block_get);
-static void tcf_block_put_final(struct work_struct *work) -{ - struct tcf_block *block = container_of(work, struct tcf_block, work); - struct tcf_chain *chain, *tmp; - - rtnl_lock(); - - /* At this point, all the chains should have refcnt == 1. */ - list_for_each_entry_safe(chain, tmp, &block->chain_list, list) - tcf_chain_put(chain); - rtnl_unlock(); - kfree(block); -} - /* XXX: Standalone actions are not allowed to jump to any chain, and bound * actions should be all removed after flushing. */ void tcf_block_put_ext(struct tcf_block *block, struct Qdisc *q, struct tcf_block_ext_info *ei) { - struct tcf_chain *chain; + struct tcf_chain *chain, *tmp;
if (!block) return; @@ -365,13 +355,11 @@ void tcf_block_put_ext(struct tcf_block
tcf_block_offload_unbind(block, q, ei);
- INIT_WORK(&block->work, tcf_block_put_final); - /* Wait for existing RCU callbacks to cool down, make sure their works - * have been queued before this. We can not flush pending works here - * because we are holding the RTNL lock. + /* At this point, all the chains should have refcnt >= 1. Block will be + * freed after all chains are gone. */ - rcu_barrier(); - tcf_queue_work(&block->work); + list_for_each_entry_safe(chain, tmp, &block->chain_list, list) + tcf_chain_put(chain); } EXPORT_SYMBOL(tcf_block_put_ext);
Patches currently in stable-queue which might be from xiyou.wangcong@gmail.com are
queue-4.15/net_sched-get-rid-of-rcu_barrier-in-tcf_block_put_ext.patch queue-4.15/cls_u32-add-missing-rcu-annotation.patch