On Wed, 2016-08-31 at 21:40 +0200, Jesper Dangaard Brouer wrote:
> I can confirm the improvement of approx 900Kpps (no wonder people have
> been complaining about DoS against UDP/DNS servers).
>
> BUT during my extensive testing, of this patch, I also think that we
> have not gotten to the bottom of this. I was expecting to see a higher
> (collective) PPS number as I add more UDP servers, but I don't.
>
> Running many UDP netperf's with command:
> super_netperf 4 -H 198.18.50.3 -l 120 -t UDP_STREAM -T 0,0 -- -m 1472 -n -N
Are you sure sender can send fast enough ?
>
> With 'top' I can see ksoftirq are still getting a higher %CPU time:
>
> PID %CPU TIME+ COMMAND
> 3 36.5 2:28.98 ksoftirqd/0
> 10724 9.6 0:01.05 netserver
> 10722 9.3 0:01.05 netserver
> 10723 9.3 0:01.05 netserver
> 10725 9.3 0:01.05 netserver
Looks much better on my machine, with "udprcv -n 4" (using 4 threads,
and 4 sockets using SO_REUSEPORT)
10755 root 20 0 34948 4 0 S 79.7 0.0 0:33.66 udprcv
3 root 20 0 0 0 0 R 19.9 0.0 0:25.49 ksoftirqd/0
Pressing 'H' in top gives :
3 root 20 0 0 0 0 R 19.9 0.0 0:47.84 ksoftirqd/0
10756 root 20 0 34948 4 0 R 19.9 0.0 0:30.76 udprcv
10757 root 20 0 34948 4 0 R 19.9 0.0 0:30.76 udprcv
10758 root 20 0 34948 4 0 S 19.9 0.0 0:30.76 udprcv
10759 root 20 0 34948 4 0 S 19.9 0.0 0:30.76 udprcv
Patch was on top of commit 071e31e254e0e0c438eecba3dba1d6e2d0da36c2
>
>
> > Since the load runs in well identified threads context, an admin can
> > more easily tune process scheduling parameters if needed.
>
> With this patch applied, I found that changing the UDP server process,
> scheduler policy to SCHED_RR or SCHED_FIFO gave me a performance boost
> from 900Kpps to 1.7Mpps, and not a single UDP packet dropped (even with
> a single UDP stream, also tested with more)
>
> Command used:
> sudo chrt --rr -p 20 $(pgrep netserver)
Sure, this is what I mentioned in my changelog : Once we properly
schedule and rely on ksoftirqd, tuning is available.
>
> The scheduling picture also change a lot:
>
> PID %CPU TIME+ COMMAND
> 10783 24.3 0:21.53 netserver
> 10784 24.3 0:21.53 netserver
> 10785 24.3 0:21.52 netserver
> 10786 24.3 0:21.50 netserver
> 3 2.7 3:12.18 ksoftirqd/0
>
>
