netdev - Re: [Patch net 01/16] net_sched: introduce a workqueue for RCU callbacks of tc filter

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Date:   Fri, 27 Oct 2017 08:37:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Chris Mi <chrism@...lanox.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jiri Pirko <jiri@...nulli.us>,
        John Fastabend <john.fastabend@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [Patch net 01/16] net_sched: introduce a workqueue for RCU
 callbacks of tc filter

On Thu, Oct 26, 2017 at 9:39 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2017-10-26 at 21:28 -0700, Cong Wang wrote:
>> On Thu, Oct 26, 2017 at 9:05 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> Paul pointed out the same.
>>
>> As I replied, this rcu_barrier() is NOT added by this patchset, it is already
>> there in current master branch.
>
> You added the rtnl_lock()  rtnl_unlock()...


Unfortunately you are wrong again, tcf_block_put() holds RTNL
in current code as well...


>
> I really do not care if hundreds of tasks (not owning rtnl) call
> rcu_barrier()...
>

You are so welcome to improve current code base, but why keep
blaming my patchset which neither introduces any rcu_barrier()
nor any RTNL? Did you even take a look at current master branch?


> Also we are still using a 4.3 based kernel, and no rcu_barrier() is used
> in filters dismantle ( unregister_tcf_proto_ops() is not used in our
> workloads )


My patchset is unfortunately not based on 4.3, this argument is totally
nonsense.

Also, filter block was introduced during v4.13.


>
> Somehow something went very wrong in net/sched in recent kernels.
>

What stops you to optimize current code?