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How deep is your buffer – Demystifying buffers and application performance

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Packet buffer memory is among the oldest topics in networking, and yet it never seems to fade in popularity. Starting from the days of buffers sized by the bandwidth delay product to what is now called "buffer bloat", from the days of 10Mbps to 100Gbps, the discussion around how deep should the buffers be never ceases to evoke opinionated responses.

In this webinar we will be joined by JR Rivers, co-founder and CTO of Cumulus Networks, a man who has designed many ultra-successful switching chips, switch products, and compute platforms, to discuss the innards of buffering. This webinar will cover data path theory, tools to evaluate network data path behavior, and the configuration variations that affect application visible outcomes.

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How deep is your buffer – Demystifying buffers and application performance

  1. 1. 1 March 14, 2017 JR Rivers | Co-founder/CTO A JOURNEY TO DEEPER UNDERSTANDING Network DataPath
  2. 2. 2 How Much Buffer – the take away If the last bit of performance matters to you, do the testing § be careful of what you read If not, take solace… …the web-scales use “small buffer” switches Network Data Path
  3. 3. 3 Tools and Knobs – Show and Tell Network Data Path cumulus@server02:~$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 16 On-line CPU(s) list: 0-15 Thread(s) per core: 2 Core(s) per socket: 4 Socket(s): 2 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 26 Model name: Intel(R) Xeon(R) CPU L5520 @ 2.27GHz Stepping: 5 CPU MHz: 1600.000 CPU max MHz: 2268.0000 CPU min MHz: 1600.0000 BogoMIPS: 4441.84 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 8192K NUMA node0 CPU(s): 0-15 Internet … 25GE attached servers, 100G interconnect server01 server02 leaf01 server03 server04 leaf03 edge01 exit01 spine01 oob-mgmt-server oob-mgmt-switch 100G 25G Link Under Test
  4. 4. 4 Tools and Knobs - iperf3 Network Data Path cumulus@server01:~$ iperf3 -c rack-edge01 -p 5201 -t 30 Connecting to host rack-edge01, port 5201 [ 4] local 10.0.1.1 port 34912 connected to 10.0.3.1 port 5201 [ ID] Interval Transfer Bandwidth Retr Cwnd [ 4] 0.00-1.00 sec 2.13 GBytes 18.3 Gbits/sec 433 888 KBytes [ 4] 1.00-2.00 sec 2.74 GBytes 23.5 Gbits/sec 0 888 KBytes [ 4] 2.00-3.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1020 KBytes [ 4] 3.00-4.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1020 KBytes [ 4] 4.00-5.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.01 MBytes [ 4] 5.00-6.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.02 MBytes [ 4] 6.00-7.00 sec 2.72 GBytes 23.4 Gbits/sec 0 1.16 MBytes [ 4] 7.00-8.00 sec 2.72 GBytes 23.4 Gbits/sec 0 1.45 MBytes [ 4] 8.00-9.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.46 MBytes [ 4] 9.00-10.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.46 MBytes [ 4] 10.00-11.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.46 MBytes [ 4] 11.00-12.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.46 MBytes [ 4] 12.00-13.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.46 MBytes [ 4] 13.00-14.00 sec 2.73 GBytes 23.5 Gbits/sec 0 1.57 MBytes [ 4] 14.00-15.00 sec 2.72 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 15.00-16.00 sec 2.73 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 16.00-17.00 sec 2.73 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 17.00-18.00 sec 2.73 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 18.00-19.00 sec 2.72 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 19.00-20.00 sec 2.73 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 20.00-21.00 sec 2.73 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 21.00-22.00 sec 2.72 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 22.00-23.00 sec 2.72 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 23.00-24.00 sec 2.72 GBytes 23.4 Gbits/sec 1 1.76 MBytes [ 4] 24.00-25.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.76 MBytes [ 4] 25.00-26.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.76 MBytes [ 4] 26.00-27.00 sec 2.74 GBytes 23.5 Gbits/sec 0 1.76 MBytes [ 4] 27.00-28.00 sec 2.73 GBytes 23.4 Gbits/sec 0 1.76 MBytes [ 4] 28.00-29.00 sec 2.65 GBytes 22.8 Gbits/sec 0 1.76 MBytes [ 4] 29.00-30.00 sec 2.73 GBytes 23.5 Gbits/sec 0 1.76 MBytes - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bandwidth Retr [ 4] 0.00-30.00 sec 81.3 GBytes 23.3 Gbits/sec 434 sender [ 4] 0.00-30.00 sec 81.3 GBytes 23.3 Gbits/sec receiver iperf Done. top - 17:10:44 up 21:55, 2 users, load average: 0.21, 0.07, 0.02 Tasks: 216 total, 1 running, 215 sleeping, 0 stopped, 0 zombie %Cpu0 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu1 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu2 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu3 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu4 : 0.7 us, 30.8 sy, 0.0 ni, 67.9 id, 0.0 wa, 0.0 hi, 0.7 si, 0.0 st %Cpu5 : 0.0 us, 4.0 sy, 0.0 ni, 95.3 id, 0.0 wa, 0.0 hi, 0.7 si, 0.0 st %Cpu6 : 0.3 us, 0.0 sy, 0.0 ni, 99.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu7 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu8 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu9 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu10 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu11 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu12 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu13 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu14 : 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st %Cpu15 : 0.4 us, 41.6 sy, 0.0 ni, 46.9 id, 0.0 wa, 0.0 hi, 11.1 si, 0.0 st KiB Mem : 74224280 total, 73448200 free, 498208 used, 277872 buff/cache KiB Swap: 75486208 total, 75486208 free, 0 used. 73183560 avail Mem Note - bandwidth is reported in TCP payload, so 23.5 Gbits/sec is wire-speed 25G Ethernet
  5. 5. 5 Tools and Knobs – tcpdump Network Data Path cumulus@edge01:~/pcaps$ sudo tcpdump -i enp4s0f1 -w single.pcap tcp port 5201 tcpdump: listening on enp4s0f1, link-type EN10MB (Ethernet), capture size 262144 bytes 1098 packets captured 1098 packets received by filter 0 packets dropped by kernel cumulus@server01:~$ iperf3 -c rack-edge01 -p 5201 -t 2 -b 50M Connecting to host rack-edge01, port 5201 [ 4] local 10.0.1.1 port 34948 connected to 10.0.3.1 port 5201 [ ID] Interval Transfer Bandwidth Retr Cwnd [ 4] 0.00-1.00 sec 5.46 MBytes 45.8 Mbits/sec 21 109 KBytes [ 4] 1.00-2.00 sec 5.88 MBytes 49.3 Mbits/sec 29 70.7 KBytes - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bandwidth Retr [ 4] 0.00-2.00 sec 11.3 MBytes 47.5 Mbits/sec 50 sender [ 4] 0.00-2.00 sec 11.3 MBytes 47.5 Mbits/sec receiver iperf Done. cumulus@edge01:~/pcaps$ tcpdump -r single.pcap reading from file single.pcap, link-type EN10MB (Ethernet) 07:52:57.600873 IP rack-server01.34946 > rack-edge01.5201: Flags [SEW], seq 1655732583, win 29200, options [mss 1460,sackOK,TS val 33182573 ecr 0,nop,wscale 7], length 0 07:52:57.600900 IP rack-edge01.5201 > rack-server01.34946: Flags [S.E], seq 319971738, ack 1655732584, win 28960, options [mss 1460,sackOK,TS val 56252912 ecr 33182573,nop,wscale 7], length 0 07:52:57.601133 IP rack-server01.34946 > rack-edge01.5201: Flags [.], ack 1, win 229, options [nop,nop,TS val 33182573 ecr 56252912], length 0 07:52:57.601160 IP rack-server01.34946 > rack-edge01.5201: Flags [P.], seq 1:38, ack 1, win 229, options [nop,nop,TS val 33182573 ecr 56252912], length 37 07:52:57.601169 IP rack-edge01.5201 > rack-server01.34946: Flags [.], ack 38, win 227, options [nop,nop,TS val 56252912 ecr 33182573], length 0 07:52:57.601213 IP rack-edge01.5201 > rack-server01.34946: Flags [P.], seq 1:2, ack 38, win 227, options [nop,nop,TS val 56252912 ecr 33182573], length 1 07:52:57.601412 IP rack-server01.34946 > rack-edge01.5201: Flags [.], ack 2, win 229, options [nop,nop,TS val 33182573 ecr 56252912], length 0 07:52:57.601419 IP rack-server01.34946 > rack-edge01.5201: Flags [P.], seq 38:42, ack 2, win 229, options [nop,nop,TS val 33182573 ecr 56252912], length 4 07:52:57.640098 IP rack-edge01.5201 > rack-server01.34946: Flags [.], ack 42, win 227, options [nop,nop,TS val 56252922 ecr 33182573], length 0 ... Need to make sure your data sources and pcap filters don’t allow drops!!!!
  6. 6. 6 Tools and Knobs - wireshark Network Data Path
  7. 7. 7 Tools and Knobs – tcpprobe Network Data Path Column Contents 1 Kernel Timestamp 2 Source_IP:port 3 Destination_IP:port 4 Packet Length 5 Send Next 6 Send Unacknowledged 7 Send Congestion Window 8 Slow Start Threshold 9 Send Window 10 Smoothed RTT 11 Receive Window cumulus@server01:~$ sudo modprobe tcp_probe port=5201 full=1 cumulus@server01:~$ sudo chmod oug+r /proc/net/tcpprobe cumulus@server01:~$ cat /proc/net/tcpprobe > /tmp/tcpprobe.out & [1] 6921 cumulus@server01:~$ iperf3 -c edge01-hs -t 5 ... snip ... [ ID] Interval Transfer Bandwidth Retr [ 4] 0.00-5.00 sec 13.0 GBytes 22.2 Gbits/sec 538 sender [ 4] 0.00-5.00 sec 12.9 GBytes 22.2 Gbits/sec receiver iperf Done. cumulus@server01:~$ kill 6921 cumulus@server01:~$ head 10 /tmp/tcpprobe.out ==> /tmp/tcpprobe.out <== 4.111198452 10.0.0.2:45520 10.0.0.5:5201 32 0x358a629a 0x3589f17a 20 2147483647 57984 142 29312 4.111461826 10.0.0.2:45520 10.0.0.5:5201 32 0x358ad962 0x358a629a 21 20 115840 161 29312 4.111731474 10.0.0.2:45520 10.0.0.5:5201 32 0x358b55d2 0x358ad962 22 20 171648 173 29312 4.112000993 10.0.0.2:45520 10.0.0.5:5201 44 0x358bd7ea 0x358b55d2 23 20 170880 185 29312 4.112037126 10.0.0.2:45520 10.0.0.5:5201 32 0x358c107a 0x358b55d2 16 16 225920 195 29312 4.112260554 10.0.0.2:45520 10.0.0.5:5201 44 0x358c5faa 0x358c1622 17 16 275200 188 29312 4.112278958 10.0.0.2:45520 10.0.0.5:5201 32 0x358c983a 0x358c1622 23 20 275200 188 29312 4.112533754 10.0.0.2:45520 10.0.0.5:5201 32 0x358ced12 0x358c326a 16 16 338944 202 29312 4.112842106 10.0.0.2:45520 10.0.0.5:5201 44 0x358d63da 0x358d03b2 17 16 396800 202 29312 4.112854569 10.0.0.2:45520 10.0.0.5:5201 32 0x358d63da 0x358d03b2 23 20 396800 202 29312 Note that the smoothed RTT is ~200 usec with no traffic!!!!!
  8. 8. 8 Tools and Knobs – TCP congestion algorithms and socket stats Network Data Path cumulus@server01:~$ ls /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp* /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_bic.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_cdg.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_dctcp.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_diag.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_highspeed.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_htcp.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_hybla.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_illinois.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_lp.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_probe.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_scalable.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_vegas.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_veno.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_westwood.ko /lib/modules/4.4.0-45-generic/kernel/net/ipv4/tcp_yeah.ko cumulus@server01:~$ cat /proc/sys/net/ipv4/tcp_congestion_control cubic cumulus@server01:~$ ss --tcp --info dport = 5201 State Recv-Q Send-Q Local Address:Port Peer Address:Port ESTAB 0 2480400 10.0.0.2:45524 10.0.0.5:5201 cubic wscale:7,7 rto:204 rtt:0.137/0.008 mss:1448 cwnd:450 ssthresh:336 bytes_acked:25460316350 segs_out:17583731 segs_in:422330 send 38049.6Mbps lastrcv:122325132 unacked:272 retrans:0/250 reordering:86 rcv_space:29200 Linux default since 2.6.19 param value wscale 7,7 rto 204 rtt 0.137/0.008 mss 1448 cwnd 450 ssthresh 336 bytes_acked 25460316350 segs_out 17583731 segs_in 422330 send 38049.6Mbps lastrcv 122325132 unacked 272 retrans 0/250 reordering 86 rcv_space 29200
  9. 9. 9 Tools and Knobs – NIC Tuning Network Data Path cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.ipv4.tcp_sack net.ipv4.tcp_sack = 1 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.core.netdev_max_backlog net.core.netdev_max_backlog = 25000 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.core.rmem_max net.core.rmem_max = 4194304 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.core.wmem_max net.core.wmem_max = 4194304 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.core.rmem_default net.core.rmem_default = 4194304 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.core.wmem_default net.core.wmem_default = 4194304 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.ipv4.tcp_rmem net.ipv4.tcp_rmem = 4096 87380 4194304 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.ipv4.tcp_wmem net.ipv4.tcp_wmem = 4096 65536 4194304 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.ipv4.tcp_low_latency net.ipv4.tcp_low_latency = 1 cumulus@edge01:/proc/sys/net/ipv4$ sysctl net.ipv4.tcp_adv_win_scale net.ipv4.tcp_adv_win_scale = 1 http://www.mellanox.com/related-docs/prod_software/Performance_Tuning_Guide_for_Mellanox_Network_Adapters.pdf
  10. 10. 10 Tools and Knobs – TCP Tuning Network Data Path cumulus@edge01:/proc/sys/net/ipv4$ ls tcp_* tcp_abort_on_overflow tcp_keepalive_probes tcp_reordering tcp_adv_win_scale tcp_keepalive_time tcp_retrans_collapse tcp_allowed_congestion_control tcp_limit_output_bytes tcp_retries1 tcp_app_win tcp_low_latency tcp_retries2 tcp_autocorking tcp_max_orphans tcp_rfc1337 tcp_available_congestion_control tcp_max_reordering tcp_rmem tcp_base_mss tcp_max_syn_backlog tcp_sack tcp_challenge_ack_limit tcp_max_tw_buckets tcp_slow_start_after_idle tcp_congestion_control tcp_mem tcp_stdurg tcp_dsack tcp_min_rtt_wlen tcp_synack_retries tcp_early_retrans tcp_min_tso_segs tcp_syncookies tcp_ecn tcp_moderate_rcvbuf tcp_syn_retries tcp_ecn_fallback tcp_mtu_probing tcp_thin_dupack tcp_fack tcp_no_metrics_save tcp_thin_linear_timeouts tcp_fastopen tcp_notsent_lowat tcp_timestamps tcp_fastopen_key tcp_orphan_retries tcp_tso_win_divisor tcp_fin_timeout tcp_pacing_ca_ratio tcp_tw_recycle tcp_frto tcp_pacing_ss_ratio tcp_tw_reuse tcp_fwmark_accept tcp_probe_interval tcp_window_scaling tcp_invalid_ratelimit tcp_probe_threshold tcp_wmem tcp_keepalive_intvl tcp_recovery tcp_workaround_signed_windows tcp_ecn - INTEGER Control use of Explicit Congestion Notification (ECN) by TCP. ECN is used only when both ends of the TCP connection indicate support for it. This feature is useful in avoiding losses due to congestion by allowing supporting routers to signal congestion before having to drop packets. Possible values are: 0 Disable ECN. Neither initiate nor accept ECN. 1 Enable ECN when requested by incoming connections and also request ECN on outgoing connection attempts. 2 Enable ECN when requested by incoming connections but do not request ECN on outgoing connections. Default: 2 https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
  11. 11. 11 Live Action Time!!!!
  12. 12. 12 Tools and Knobs – What’s next for me Find/write a good ”mice” traffic generator § modify iperf3 to include mean-time-to-completion with blocks DCTCP with both ECN and Priority Flow Control § High performance fabrics combine end-to-end congestion management and lossless links Infiniband, Fibre Channel, PCIe, NumaLink, etc Network Data Path
  13. 13. 13 How Much Buffer – the take away If the last bit of performance matters to you, do the testing § be careful of what you read If not, take solace… …the web-scales use “small buffer” switches Network Data Path
  14. 14. 14 Thank you! Visit us at cumulusnetworks.com or follow us @cumulusnetworks © 2017 Cumulus Networks. Cumulus Networks, the Cumulus Networks Logo, and Cumulus Linux are trademarks or registered trademarks of Cumulus Networks, Inc. or its affiliates in the U.S. and other countries. Other names may be trademarks of their respective owners. The registered trademark Linux® is used pursuant to a sublicense from LMI, the exclusive licensee of Linus Torvalds, owner of the mark on a world-wide basis.

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