On 2021/3/17 21:45, Jason A. Donenfeld wrote: > On 3/17/21, Toke Høiland-Jørgensen <t...@redhat.com> wrote: >> Cong Wang <xiyou.wangc...@gmail.com> writes: >> >>> On Mon, Mar 15, 2021 at 2:07 PM Jakub Kicinski <k...@kernel.org> 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 :) > > That offer definitely still stands. Generalization sounds like a lot of fun. > > Keep in mind though that it's an eventually consistent queue, not an > immediately consistent one, so that might not match all use cases. It > works with wg because we always trigger the reader thread anew when it > finishes, but that doesn't apply to everyone's queueing setup.
Thanks for mentioning this. "multi-producer, single-consumer" seems to match the lockless qdisc's paradigm too, for now concurrent enqueuing/dequeuing to the pfifo_fast's queues() is not allowed, it is protected by producer_lock or consumer_lock. So it would be good to has lockless concurrent enqueuing, while dequeuing can be protected by qdisc_lock() or q->seqlock, which meets the "multi-producer, single-consumer" paradigm. But right now lockless qdisc has some packet stuck problem, which I tried to fix in [1]. If the packet stuck problem for lockless qdisc can be fixed, and we can do more optimization on lockless qdisc, including the one you mention:) 1.https://patchwork.kernel.org/project/netdevbpf/patch/1616050402-37023-1-git-send-email-linyunsh...@huawei.com/ > _______________________________________________ > Linuxarm mailing list -- linux...@openeuler.org > To unsubscribe send an email to linuxarm-le...@openeuler.org >