On 3/15/21 4:10 AM, Yunsheng Lin wrote: > Currently pfifo_fast has both TCQ_F_CAN_BYPASS and TCQ_F_NOLOCK > flag set, but queue discipline by-pass does not work for lockless > qdisc because skb is always enqueued to qdisc even when the qdisc > is empty, see __dev_xmit_skb(). > > This patch calls sch_direct_xmit() to transmit the skb directly > to the driver for empty lockless qdisc too, which aviod enqueuing > and dequeuing operation. qdisc->empty is set to false whenever a > skb is enqueued, see pfifo_fast_enqueue(), and is set to true when > skb dequeuing return NULL, see pfifo_fast_dequeue(), a spinlock is > added to avoid the race between enqueue/dequeue and qdisc->empty > setting. > > If there is requeued skb in q->gso_skb, and qdisc->empty is true, > do not allow bypassing requeued skb. enqueuing and dequeuing in > q->gso_skb is always protected by qdisc->seqlock, so is the access > of q->gso_skb by skb_queue_empty(); > > Also, qdisc is scheduled at the end of qdisc_run_end() when q->empty > is false to avoid packet stuck problem. > > The performance for ip_forward test increases about 10% with this > patch. > > Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx> I gave it a short test on a single core imx. No problem here. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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