netdev - Re: [PATCH net-next v4 07/17] net: sched: protect filter_chain list with filter_chain

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Date:   Wed, 20 Feb 2019 14:43:21 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Ido Schimmel <idosch@...sch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH net-next v4 07/17] net: sched: protect filter_chain list
 with filter_chain_lock mutex

On Tue, Feb 19, 2019 at 4:31 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
>
> On Tue 19 Feb 2019 at 05:26, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Fri, Feb 15, 2019 at 7:35 AM Vlad Buslov <vladbu@...lanox.com> wrote:
> >>
> >> Another problem that I found in cls_fw and cls_route is that they set
> >> arg->stop when empty. Both of them have code unchanged since it was
> >> committed initially in 2005 so I assume this convention is no longer
> >> relevant because all other classifiers don't do that (they only set
> >> arg->stop when arg->fn returns negative value).
> >>
> >
> > The question is why do you want to use arg->stop==0 as
> > an indication for emptiness? Isn't what arg->count==0
> > supposed to be?
>
> Good question! I initially wanted to implement it like that, but
> reconsidered because iterating through all filters on classifier to
> count them is O(N), and terminating on first filter and relying on
> arg->stop==1 is constant time. Making function that is called
> "tcf_proto_is_empty" linear on number of filters seemed sloppy to me...

Good point, however arg->stop _was_ supposed to set only when
error happens. Probably you want a new arg here to stop on the first
entry.