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Date: Mon, 25 May 2015 10:53:38 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: "John A. Sullivan III" <jsullivan@...nsourcedevel.com> Cc: netdev@...r.kernel.org Subject: Re: TCP window auto-tuning sub-optimal in GRE tunnel On Mon, 2015-05-25 at 09:58 -0700, Eric Dumazet wrote: > 1) Non GRE session > > lpaa23:~# DUMP_TCP_INFO=1 ./netperf -H lpaa24 -Cc -t OMNI > OMNI Send TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to lpaa24.prod.google.com () port 0 AF_INET > tcpi_rto 201000 tcpi_ato 0 tcpi_pmtu 1500 tcpi_rcv_ssthresh 29200 > tcpi_rtt 70 tcpi_rttvar 7 tcpi_snd_ssthresh 221 tpci_snd_cwnd 258 > tcpi_reordering 3 tcpi_total_retrans 711 > Local Remote Local Elapsed Throughput Throughput Local Local Remote Remote Local Remote Service > Send Socket Recv Socket Send Time Units CPU CPU CPU CPU Service Service Demand > Size Size Size (sec) Util Util Util Util Demand Demand Units > Final Final % Method % Method > 1912320 6291456 16384 10.00 22386.89 10^6bits/s 1.20 S 2.60 S 0.211 0.456 usec/KB > > 2) GRE session > > lpaa23:~# DUMP_TCP_INFO=1 ./netperf -H 7.7.7.24 -Cc -t OMNI > OMNI Send TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 7.7.7.24 () port 0 AF_INET > tcpi_rto 201000 tcpi_ato 0 tcpi_pmtu 1500 tcpi_rcv_ssthresh 29200 > tcpi_rtt 76 tcpi_rttvar 7 tcpi_snd_ssthresh 176 tpci_snd_cwnd 249 > tcpi_reordering 3 tcpi_total_retrans 819 > Local Remote Local Elapsed Throughput Throughput Local Local Remote Remote Local Remote Service > Send Socket Recv Socket Send Time Units CPU CPU CPU CPU Service Service Demand > Size Size Size (sec) Util Util Util Util Demand Demand Units > Final Final % Method % Method > 1815552 6291456 16384 10.00 22420.88 10^6bits/s 1.01 S 3.44 S 0.177 0.603 usec/KB Scratch these numbers, they were quite wrong (7.7.7.24 was not using a GRE tunnel) Correct experiment : 1) No GRE tunnel lpaa23:~# DUMP_TCP_INFO=1 ./netperf -H lpaa24 -Cc -t OMNI -l 10 OMNI Send TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to lpaa24.prod.google.com () port 0 AF_INET tcpi_rto 201000 tcpi_ato 0 tcpi_pmtu 1500 tcpi_rcv_ssthresh 29200 tcpi_rtt 82 tcpi_rttvar 11 tcpi_snd_ssthresh 356 tpci_snd_cwnd 358 tcpi_reordering 3 tcpi_total_retrans 288 Local Remote Local Elapsed Throughput Throughput Local Local Remote Remote Local Remote Service Send Socket Recv Socket Send Time Units CPU CPU CPU CPU Service Service Demand Size Size Size (sec) Util Util Util Util Demand Demand Units Final Final % Method % Method 2492928 6291456 16384 10.03 31426.29 10^6bits/s 1.14 S 4.82 S 0.143 0.603 usec/KB 2) GRE tunnel ---------------------------------------------- lpaa23:~# DUMP_TCP_INFO=1 ./netperf -H 10.7.8.152 -Cc -t OMNI -l 10 OMNI Send TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.7.8.152 () port 0 AF_INET tcpi_rto 201000 tcpi_ato 0 tcpi_pmtu 1476 tcpi_rcv_ssthresh 28720 tcpi_rtt 165 tcpi_rttvar 27 tcpi_snd_ssthresh 263 tpci_snd_cwnd 264 tcpi_reordering 81 tcpi_total_retrans 26 Local Remote Local Elapsed Throughput Throughput Local Local Remote Remote Local Remote Service Send Socket Recv Socket Send Time Units CPU CPU CPU CPU Service Service Demand Size Size Size (sec) Util Util Util Util Demand Demand Units Final Final % Method % Method 1216512 6291456 16384 10.00 8471.24 10^6bits/s 2.82 S 2.56 S 1.308 1.190 usec/KB Bottleneck here is the sender, because NIC does not support GRE/TSO, so we spend lot of time doing segmentation and TX checksum, consuming a full cpu core. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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