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;a=summary
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@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Wed Feb 7 11:29:33 PST 2018
From: Cong Wang <xiyou.wangcong@xxxxxxxxx>
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@xxxxxxxxx>
[ 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@xxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jiri Pirko <jiri@xxxxxxxxxxxx>
Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxx 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