Re: Packet gets stuck in NOLOCK pfifo_fast qdisc

[Cong Wang]

On Thu, Sep 3, 2020 at 1:40 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
>
> On Wed, 2020-09-02 at 22:01 -0700, Cong Wang wrote:
> > Can you test the attached one-line fix? I think we are overthinking,
> > probably all
> > we need here is a busy wait.
>
> I think that will solve, but I also think that will kill NOLOCK
> performances due to really increased contention.

Yeah, we somehow end up with more locks (seqlock, skb array lock)
for lockless qdisc. What an irony... ;)

>
> At this point I fear we could consider reverting the NOLOCK stuff.
> I personally would hate doing so, but it looks like NOLOCK benefits are
> outweighed by its issues.

I agree, NOLOCK brings more pains than gains. There are many race
conditions hidden in generic qdisc layer, another one is enqueue vs.
reset which is being discussed in another thread.

Thanks.