netdev - Re: [PATCH net-next v6 01/11] net: sched: use rcu for action cookie update

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Message-ID: <CAM_iQpX6rV+2=D6WR4KVR1cDfgKL2iR9+9T9-9CJvY8xnYBSgQ@mail.gmail.com>
Date:   Fri, 13 Jul 2018 17:14:33 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Vlad Buslov <vladbu@...lanox.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yevgeny Kliteynik <kliteyn@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH net-next v6 01/11] net: sched: use rcu for action cookie update

On Fri, Jul 13, 2018 at 3:11 PM David Miller <davem@...emloft.net> wrote:
>
> From: Cong Wang <xiyou.wangcong@...il.com>
> Date: Fri, 13 Jul 2018 14:51:15 -0700
>
> > Can we at least agree you have no justification for this change in
> > this changelog?
>
> He stated that he wishes to make this subsystem more lockless, and he
> cannot do that without making the action cookie handling use RCU.

This isn't enough given RCU writers are recommended (subject
to exceptions) to have locks. Let's move this discussion on patch
00/11 where I provided more details. :)

>
> I agree with the stated goal, and the necessity of this kind of change.
>
> Therefore I applied the patch.
>
> I really don't see what the problem is.
>
> I also gave a couple days for this patch set to get reviewed.  If you
> have a problem, please respond to the patch posting.  When I see nobody
> is reviewing, that is when I step in and make my own judgment.
>
> So when you want your objection to be heard, please do so in a timely
> manner.  That helps all of us.

I 100% understand given how much workload you have. I am not even
saying to revert or something.

My only complain is the goal of lockless is very hard or nearly
impossible to achieve, unless there is some secret hiding from me.
And I am trying to get it exposed in my response to 00/11, by offering
an opportunity to prove I am wrong! :)

The problem with this patch, 01/11, is trivial comparing to the
discussion in 00/11, that is crucial for whether the whole patchset(s)
makes sense.

Thanks for taking care of it anyway!