Re: [Linuxarm] Re: [PATCH net v6 3/3] net: sched: fix tx action reschedule issue with stopped queue

On Wed, 12 May 2021 11:34:55 +0800 Yunsheng Lin wrote:

quoted

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.