netdev - Re: [Patch net-next v2] net_sched: introduce tracepoint trace_qdisc

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Date:   Sun, 11 Jul 2021 21:19:56 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Tonghao Zhang <xiangxia.m.yue@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Qitao Xu <qitao.xu@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net-next v2] net_sched: introduce tracepoint trace_qdisc_enqueue()

On Sun, Jul 11, 2021 at 9:12 PM Tonghao Zhang <xiangxia.m.yue@...il.com> wrote:
>
> On Mon, Jul 12, 2021 at 12:02 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > On Sun, Jul 11, 2021 at 8:49 PM Tonghao Zhang <xiangxia.m.yue@...il.com> wrote:
> > >
> > > On Mon, Jul 12, 2021 at 11:39 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
> > > >
> > > > On Sun, Jul 11, 2021 at 8:36 PM Tonghao Zhang <xiangxia.m.yue@...il.com> wrote:
> > > > >
> > > > > On Mon, Jul 12, 2021 at 11:23 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
> > > > > > Sure, in that case a different packet is dropped, once again you
> > > > > > can trace it with kfree_skb() if you want. What's the problem?
> > > > > It's ok, but we can make it better. Yunsheng Lin may have explained why?
> > > >
> > > > Why it is better to trace dropped packets both in enqueue and in kfree_skb()?
> > > I mean we can use one tracepoint to know what happened in the queue,
> > > not necessary to trace enqueue and  kfree_skb()
> >
> > This is wrong, packets can be dropped for other reasons too, tracing
> no matter where the packet is dropped, we should allow user to know
> whether dropped in the enqueue.  and the
> what the return value.

Again you can know it by kfree_skb(). And you can not avoid
kfree_skb() no matter how you change enqueue. So, I don't see your
argument of saving kfree_skb() makes any sense here.

Thanks.