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Donenfeld" Subject: Re: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc In-Reply-To: References: <1615603667-22568-1-git-send-email-linyunsheng@huawei.com> <1615777818-13969-1-git-send-email-linyunsheng@huawei.com> <20210315115332.1647e92b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Wed, 17 Mar 2021 14:35:40 +0100 Message-ID: <87eegddhsj.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org Cong Wang writes: > On Mon, Mar 15, 2021 at 2:07 PM Jakub Kicinski 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