Cc += linux-can@xxxxxxxxxxxxxxx On 3/14/21 1:03 AM, Vladimir Oltean wrote: > On Sat, Mar 13, 2021 at 10:47:47AM +0800, 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 calles 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, and is set to true when skb dequeuing return NULL, >> see pfifo_fast_dequeue(). >> >> 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 can confirm the ~10% IP forwarding throughput improvement brought by > this patch, but as you might be aware, there was a previous attempt to > add qdisc bypass to pfifo_fast by Paolo Abeni: > https://lore.kernel.org/netdev/661cc33a-5f65-2769-cc1a-65791cb4b131@xxxxxxxxxxxxxx/ > It was reverted because TX reordering was observed with SocketCAN > (although, presumably it should also be seen with Ethernet and such). Thanks for testing that, I just stumbled over this patch by accident. 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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