Re: [Linuxarm] Re: [PATCH net v6 3/3] net: sched: fix tx action reschedule issue with stopped queue
From: Jakub Kicinski
Date: Wed May 12 2021 - 16:34:58 EST
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.