Re: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc

[Toke Høiland-Jørgensen]

Cong Wang <xiyou.wangcong@xxxxxxxxx> writes:

> On Mon, Mar 15, 2021 at 2:07 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>>
>> I thought pfifo was supposed to be "lockless" and this change
>> re-introduces a lock between producer and consumer, no?
>
> It has never been truly lockless, it uses two spinlocks in the ring buffer
> implementation, and it introduced a q->seqlock recently, with this patch
> now we have priv->lock, 4 locks in total. So our "lockless" qdisc ends
> up having more locks than others. ;) I don't think we are going to a
> right direction...

Just a thought, have you guys considered adopting the lockless MSPC ring
buffer recently introduced into Wireguard in commit:

8b5553ace83c ("wireguard: queueing: get rid of per-peer ring buffers")

Jason indicated he was willing to work on generalising it into a
reusable library if there was a use case for it. I haven't quite though
through the details of whether this would be such a use case, but
figured I'd at least mention it :)

-Toke