Subject: Re: [PATCH v2 net-next 0/4] udp: receive path optimizations

From: Jesper Dangaard Brouer <[email-masked]>
Date: Thu, 8 Dec 2016 22:17:16 +0100

On Thu, 8 Dec 2016 21:48:19 +0100
Jesper Dangaard Brouer <[email-masked]> wrote:

> On Thu,  8 Dec 2016 09:38:55 -0800
> Eric Dumazet <[email-masked]> wrote:
> 
> > This patch series provides about 100 % performance increase under flood.   
> 
> Could you please explain a bit more about what kind of testing you are
> doing that can show 100% performance improvement?
> 
> I've tested this patchset and my tests show *huge* speeds ups, but
> reaping the performance benefit depend heavily on setup and enabling
> the right UDP socket settings, and most importantly where the
> performance bottleneck is: ksoftirqd(producer) or udp_sink(consumer).
> 
> Basic setup: Unload all netfilter, and enable ip_early_demux.
>  sysctl net/ipv4/ip_early_demux=1
> 
> Test generator pktgen UDP packets single flow, 50Gbit/s mlx5 NICs.
>  - Vary packet size between 64 and 1514.

Below, I've added the baseline tests.

Baseline test on net-next at commit c9fba3ed3a4

> Packet-size: 64
> $ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7))
>                                 ns/pkt  pps             cycles/pkt
> recvMmsg/32  	run: 0 10000000	537.70	1859756.90	2155
> recvmsg   	run: 0 10000000	510.84	1957541.83	2047
> read      	run: 0 10000000	583.40	1714077.14	2338
> recvfrom  	run: 0 10000000	600.09	1666411.49	2405

Packet-size: 64 (baseline)
$ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7))
recvMmsg/32  	run: 0 10000000	499.75	2001016.09	2003
recvmsg   	run: 0 10000000	455.84	2193740.92	1827
read      	run: 0 10000000	566.99	1763703.49	2272
recvfrom  	run: 0 10000000	581.02	1721098.87	2328

> The ksoftirq thread "cost" more than udp_sink, which is idle, and UDP
> queue does not get full-enough. Thus, patchset does not have any
> effect.
> 
> 
> Try to increase pktgen packet size, as this increase the copy cost of
> udp_sink.  Thus, a queue can now form, and udp_sink CPU almost have no
> idle cycles.  The "read" and "readfrom" did experience some idle
> cycles.
> 
> Packet-size: 1514
> $ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7))
>                                 ns/pkt  pps             cycles/pkt
> recvMmsg/32  	run: 0 10000000	435.88	2294204.11	1747
> recvmsg   	run: 0 10000000	458.06	2183100.64	1835
> read      	run: 0 10000000	520.34	1921826.18	2085
> recvfrom  	run: 0 10000000	515.48	1939935.27	2066

Packet-size: 1514 (baseline)
$ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7))
recvMmsg/32  	run: 0 10000000	453.88	2203231.81	1819
recvmsg   	run: 0 10000000	488.31	2047869.13	1957
read      	run: 0 10000000	480.99	2079058.69	1927
recvfrom  	run: 0 10000000	522.64	1913349.26	2094

> Next trick connected UDP:
> 
> Use connected UDP socket (combined with ip_early_demux), removes the
> FIB_lookup from the ksoftirq, and cause tipping point to be better.
> 
> Packet-size: 64
> $ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7)) --connect
>                                 ns/pkt  pps             cycles/pkt
> recvMmsg/32  	run: 0 10000000	391.18	2556361.62	1567
> recvmsg   	run: 0 10000000	422.95	2364349.69	1695
> read      	run: 0 10000000	425.29	2351338.10	1704
> recvfrom  	run: 0 10000000	476.74	2097577.57	1910

Packet-size: 64 (baseline)
$ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7)) --connect
recvMmsg/32  	run: 0 10000000	438.55	2280255.77	1757
recvmsg   	run: 0 10000000	496.73	2013156.99	1990
read      	run: 0 10000000	412.17	2426170.58	1652
recvfrom  	run: 0 10000000	471.77	2119662.99	1890

> Change/increase packet size:
> 
> Packet-size: 1514
> $ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7)) --connect
>                                 ns/pkt  pps             cycles/pkt
> recvMmsg/32  	run: 0 10000000	457.56	2185481.94	1833
> recvmsg   	run: 0 10000000	479.42	2085837.49	1921
> read      	run: 0 10000000	398.05	2512233.13	1595
> recvfrom  	run: 0 10000000	391.07	2557096.95	1567

Packet-size: 1514 (baseline)
$ sudo taskset -c 4 ./udp_sink --port 9 --count $((10**7)) --connect
recvMmsg/32  	run: 0 10000000	491.11	2036205.63	1968
recvmsg   	run: 0 10000000	514.37	1944138.31	2061
read      	run: 0 10000000	444.02	2252147.84	1779
recvfrom  	run: 0 10000000	426.58	2344247.20	1709

> A bit strange, changing the packet size, flipped what is the fastest
> syscall.
> 
> It is also interesting to see that ksoftirq limit is:
> 
> Result from "nstat" while using recvmsg, show that ksoftirq is
> handling 2.6 Mpps, and consumer/udp_sink is bottleneck with 2Mpps.
> 
> [skylake ~]$ nstat > /dev/null && sleep 1  && nstat
> #kernel
> IpInReceives                    2667577            0.0
> IpInDelivers                    2667577            0.0
> UdpInDatagrams                  2083580            0.0
> UdpInErrors                     583995             0.0
> UdpRcvbufErrors                 583995             0.0
> IpExtInOctets                   4001340000         0.0
> IpExtInNoECTPkts                2667559            0.0

(baseline 1514 bytes recvmsg)
$ nstat > /dev/null && sleep 1  && nstat
#kernel
IpInReceives                    2702424            0.0
IpInDelivers                    2702423            0.0
UdpInDatagrams                  1950184            0.0
UdpInErrors                     752239             0.0
UdpRcvbufErrors                 752239             0.0
IpExtInOctets                   4053642000         0.0
IpExtInNoECTPkts                2702428            0.0

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer