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

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Date:   Tue, 17 Jul 2018 13:46:42 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        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 Mon, Jul 16, 2018 at 1:31 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
>
> On Fri 13 Jul 2018 at 21:51, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Fri, Jul 13, 2018 at 6:30 AM Vlad Buslov <vladbu@...lanox.com> wrote:
> >>
> >>
> >> On Fri 13 Jul 2018 at 03:52, Cong Wang <xiyou.wangcong@...il.com> wrote:
> >> > On Thu, Jul 5, 2018 at 7:24 AM Vlad Buslov <vladbu@...lanox.com> wrote:
> >> >>
> >> >> Implement functions to atomically update and free action cookie
> >> >> using rcu mechanism.
> >> >
> >> > Without stating any reason..... Is this even a changelog?
> >>
> >> Yes, it is.
> >
> > What do you expect in a changelog generally? Repeating what
> > your code does? Thanks but we don't even want to read any code
> > unless the need of this code is reasonably justified.
>
> In my cover letter:
>  - Motivation for patchset is presented in first paragraph.
>  - Problems that prevent us from removing rtnl lock dependency are
>  described, problem 3 is about cookie pointer.
>  - In implementation section, point 3 presents solution for that
>  problem.


Do you want to use cover letter as a changelog for all patches in
your patchset? Seriously? :)

Every patch is your patchset is unique, because you are not fixing
a problem can be expressed by a pattern.

Given how hard lockless is generally, probably you even can't
find out a pattern. If you really do, I am happy to learn!


>
> >
> > Can we at least agree you have no justification for this change
> > in this changelog? Or you believe this patch is as trivial as
> > a white space change which doesn't need a justification?
>
> Cong, from your last letter I understand that you want to have
> justification specifically for using atomic operation in this particular
> patch. I agree with you that I should have explained it in more details.
> I found a lot of prior art for same or similar atomic ops usage for rcu
> pointers(examples in my previous mail) and assumed it to be trivial, but
> now I understand that I was wrong in this case.

Thanks for having an agreement!

I expect to see more detailed changelog in your future patches! :)