dummynet dropping too many packets

[rihad]

Robert Watson wrote:
> I would suggest making just the HZ -> 4000 change for now and see how
> it goes.
> 
2018 users online, 73 drops have just occurred.
p.s.: already 123 drops.
It will only get worse after some time.

Traffic load: 440-450 mbps.

top -HS:
last pid: 68314;  load averages:  1.35,  1.22,  1.25
                             up 0+05:13:28  17:53:49
145 processes: 11 running, 118 sleeping, 16 waiting
CPU:  1.4% user,  0.0% nice,  2.8% system, 10.3% interrupt, 85.5% idle
Mem: 1337M Active, 1683M Inact, 355M Wired, 40K Cache, 214M Buf, 560M Free
Swap: 2048M Total, 2048M Free

   PID USERNAME   PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAND
    14 root       171 ki31     0K    16K CPU4   4 257:35 99.41% idle: cpu4
    12 root       171 ki31     0K    16K RUN    6 286:39 98.14% idle: cpu6
    18 root       171 ki31     0K    16K RUN    0 225:16 92.72% idle: cpu0
    15 root       171 ki31     0K    16K RUN    3 255:35 90.04% idle: cpu3
    16 root       171 ki31     0K    16K CPU2   2 272:04 87.40% idle: cpu2
    13 root       171 ki31     0K    16K CPU5   5 260:52 81.69% idle: cpu5
    17 root       171 ki31     0K    16K CPU1   1 239:06 75.29% idle: cpu1
    21 root       -44    -     0K    16K CPU7   7 108:49 57.37% swi1: net
    11 root       171 ki31     0K    16K CPU7   7 267:48 49.02% idle: cpu7
    29 root       -68    -     0K    16K WAIT   1  41:45 20.90% irq256: bce0
   470 root       -68    -     0K    16K -      5  27:01  9.18% dummynet
    19 root       -32    -     0K    16K WAIT   1  16:13  6.59% swi4:
clock sio
    31 root       -68    -     0K    16K WAIT   2   9:35  4.35% irq257: bce1

> Robert Watson wrote:
> Suggestions like increasing timer resolution are intended to spread
> out the injection of packets by dummynet to attempt to reduce the
> peaks of burstiness that occur when multiple queues inject packets in
> a burst that exceeds the queue depth supported by combined hardware
> descriptor rings and software transmit queue.

How to tweak the software transmit queue?


P.S.: still only 123 drops (while io_pkt_drop: 0, intr_queue_drops: 0), 
but it was a warning.