On Wed, 12 May 2021 11:34:55 +0800 Yunsheng Lin wrote: > > This is indeed the idiomatic way of dealing with Tx queue stopping race, > > but it's a bit of code to sprinkle around. My vote would be option 1. > > I had done some performance testing to see which is better, tested using > pktgen and dummy netdev with pfifo_fast qdisc attached: > > unit: Mpps > > threads V6 V6 + option 1 V6 + option 3 > 1 2.60 2.54 2.60 > 2 3.86 3.84 3.84 > 4 5.56 5.50 5.51 > 8 2.79 2.77 2.77 > 16 2.23 2.24 2.22 > > So it seems the netif_xmit_frozen_or_stopped checking overhead for non-stopped queue > is noticable for 1 pktgen thread. > > And the performance increase for V6 + option 1 with 16 pktgen threads is because of > "clear_bit(__QDISC_STATE_MISSED, &qdisc->state)" at the end of qdisc_run_end(), which > may avoid the another round of dequeuing in the pfifo_fast_dequeue(). And adding the > "clear_bit(__QDISC_STATE_MISSED, &qdisc->state)" for V6 + option 3, the data for > 16 pktgen thread also go up to 2.24Mpps. > > > So it seems V6 + option 3 with "clear_bit(__QDISC_STATE_MISSED, &qdisc->state)" at > the end of qdisc_run_end() is better? Alright, sounds good.
