SO_SNDBUF, SO_RCVBUF and impact on loopback transfer

[nikkoara]

FWIW, I have stumbled upon a situation where transfer of DICOM files between storescp/storescu on loopback, was very, very slow, approx 2 min for a 25M file.

I profiled storescp and storescu and that showed no time is inefficiently spent in the application. iperf shows nothing remarkable. Netcat transfers of arbitrary files via loopback are as fast as expected for this computer. I sniffed the traffic between the storescp and storescu instances and that shows, more often than not, "TCP Window full" warnings from wireshark. The amount of warnings is proportional with the slowdown. I experimented with various pdu settings for each app, from 8k up to 128K but they all show the same slow throughput with pretty much the same small variations between runs. Interestingly, transfers between storescu and storescp instances sitting on different computers (one being the affected laptop) look normal.

Reading the code I came upon the setTCPBufferLength function. I disabled the code that sets the buffer sizes and that solved the performance problem. I also do not see a degradation of transfer performance through the regular network interfaces, after the change.

[J. Riesmeier]

That's strange. Could you give us more details on the system environment?

[nikkoara]

Sure. It's a modern ultrabook running the latest Ubuntu, fully up to date. I have built DCMTK off the 20131114 snapshot, in Release configuration.

[joe@ncc1701:~]$ uname -a
Linux ncc1701 3.13.0-29-generic #53-Ubuntu SMP Wed Jun 4 21:00:20 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

[joe@ncc1701:~]$ lspci
00:00.0 Host bridge: Intel Corporation Haswell-ULT DRAM Controller (rev 09)
00:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated Graphics Controller (rev 09)
00:03.0 Audio device: Intel Corporation Haswell-ULT HD Audio Controller (rev 09)
00:04.0 Signal processing controller: Intel Corporation Device 0a03 (rev 09)
00:14.0 USB controller: Intel Corporation Lynx Point-LP USB xHCI HC (rev 04)
00:16.0 Communication controller: Intel Corporation Lynx Point-LP HECI #0 (rev 04)
00:1b.0 Audio device: Intel Corporation Lynx Point-LP HD Audio Controller (rev 04)
00:1c.0 PCI bridge: Intel Corporation Lynx Point-LP PCI Express Root Port 1 (rev e4)
00:1d.0 USB controller: Intel Corporation Lynx Point-LP USB EHCI #1 (rev 04)
00:1f.0 ISA bridge: Intel Corporation Lynx Point-LP LPC Controller (rev 04)
00:1f.2 SATA controller: Intel Corporation Lynx Point-LP SATA Controller 1 [AHCI mode] (rev 04)
00:1f.3 SMBus: Intel Corporation Lynx Point-LP SMBus Controller (rev 04)
00:1f.6 Signal processing controller: Intel Corporation Lynx Point-LP Thermal (rev 04)
01:00.0 Network controller: Intel Corporation Wireless 7260 (rev 6b)

[joe@ncc1701:~]$ file /lib/x86_64-linux-gnu/libc-2.19.so
/lib/x86_64-linux-gnu/libc-2.19.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), BuildID[sha1]=b571f83a8a6f5bb22d3558cddda9f943a2a67fd1, for GNU/Linux 2.6.24, stripped

[joe@ncc1701:~]$ /lib/x86_64-linux-gnu/libc-2.19.so
GNU C Library (Ubuntu EGLIBC 2.19-0ubuntu6) stable release version 2.19, by Roland McGrath et al.
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.8.2.
Compiled on a Linux 3.13.9 system on 2014-04-12.
Available extensions:
crypt add-on version 2.1 by Michael Glad and others
GNU Libidn by Simon Josefsson
Native POSIX Threads Library by Ulrich Drepper et al
BIND-8.2.3-T5B
libc ABIs: UNIQUE IFUNC
For bug reporting instructions, please see:
<https://bugs.launchpad.net/ubuntu/+source/eglibc/+bugs>.

[joe@ncc1701:~]$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.8.2-19ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1)

[joe@ncc1701:~]$ sudo sysctl -a | grep \^net
[sudo] password for joe:
net.core.bpf_jit_enable = 0
net.core.busy_poll = 0
net.core.busy_read = 0
net.core.default_qdisc = pfifo_fast
net.core.dev_weight = 64
net.core.flow_limit_cpu_bitmap = 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000
net.core.flow_limit_table_len = 4096
net.core.message_burst = 10
net.core.message_cost = 5
net.core.netdev_budget = 300
net.core.netdev_max_backlog = 1000
net.core.netdev_tstamp_prequeue = 1
net.core.optmem_max = 20480
net.core.rmem_default = 212992
net.core.rmem_max = 212992
net.core.rps_sock_flow_entries = 0
net.core.somaxconn = 128
net.core.warnings = 1
net.core.wmem_default = 212992
net.core.wmem_max = 212992
net.core.xfrm_acq_expires = 30
net.core.xfrm_aevent_etime = 10
net.core.xfrm_aevent_rseqth = 2
net.core.xfrm_larval_drop = 1
net.ipv4.cipso_cache_bucket_size = 10
net.ipv4.cipso_cache_enable = 1
net.ipv4.cipso_rbm_optfmt = 0
net.ipv4.cipso_rbm_strictvalid = 1
net.ipv4.conf.all.accept_local = 0
net.ipv4.conf.all.accept_redirects = 1
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.all.arp_accept = 0
net.ipv4.conf.all.arp_announce = 0
net.ipv4.conf.all.arp_filter = 0
net.ipv4.conf.all.arp_ignore = 0
net.ipv4.conf.all.arp_notify = 0
net.ipv4.conf.all.bootp_relay = 0
net.ipv4.conf.all.disable_policy = 0
net.ipv4.conf.all.disable_xfrm = 0
net.ipv4.conf.all.force_igmp_version = 0
net.ipv4.conf.all.forwarding = 0
net.ipv4.conf.all.igmpv2_unsolicited_report_interval = 10000
net.ipv4.conf.all.igmpv3_unsolicited_report_interval = 1000
net.ipv4.conf.all.log_martians = 0
net.ipv4.conf.all.mc_forwarding = 0
net.ipv4.conf.all.medium_id = 0
net.ipv4.conf.all.promote_secondaries = 0
net.ipv4.conf.all.proxy_arp = 0
net.ipv4.conf.all.proxy_arp_pvlan = 0
net.ipv4.conf.all.route_localnet = 0
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.all.secure_redirects = 1
net.ipv4.conf.all.send_redirects = 1
net.ipv4.conf.all.shared_media = 1
net.ipv4.conf.all.src_valid_mark = 0
net.ipv4.conf.all.tag = 0
net.ipv4.conf.default.accept_local = 0
net.ipv4.conf.default.accept_redirects = 1
net.ipv4.conf.default.accept_source_route = 1
net.ipv4.conf.default.arp_accept = 0
net.ipv4.conf.default.arp_announce = 0
net.ipv4.conf.default.arp_filter = 0
net.ipv4.conf.default.arp_ignore = 0
net.ipv4.conf.default.arp_notify = 0
net.ipv4.conf.default.bootp_relay = 0
net.ipv4.conf.default.disable_policy = 0
net.ipv4.conf.default.disable_xfrm = 0
net.ipv4.conf.default.force_igmp_version = 0
net.ipv4.conf.default.forwarding = 0
net.ipv4.conf.default.igmpv2_unsolicited_report_interval = 10000
net.ipv4.conf.default.igmpv3_unsolicited_report_interval = 1000
net.ipv4.conf.default.log_martians = 0
net.ipv4.conf.default.mc_forwarding = 0
net.ipv4.conf.default.medium_id = 0
net.ipv4.conf.default.promote_secondaries = 0
net.ipv4.conf.default.proxy_arp = 0
net.ipv4.conf.default.proxy_arp_pvlan = 0
net.ipv4.conf.default.route_localnet = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.secure_redirects = 1
net.ipv4.conf.default.send_redirects = 1
net.ipv4.conf.default.shared_media = 1
net.ipv4.conf.default.src_valid_mark = 0
net.ipv4.conf.default.tag = 0
net.ipv4.conf.lo.accept_local = 0
net.ipv4.conf.lo.accept_redirects = 1
net.ipv4.conf.lo.accept_source_route = 1
net.ipv4.conf.lo.arp_accept = 0
net.ipv4.conf.lo.arp_announce = 0
net.ipv4.conf.lo.arp_filter = 0
net.ipv4.conf.lo.arp_ignore = 0
net.ipv4.conf.lo.arp_notify = 0
net.ipv4.conf.lo.bootp_relay = 0
net.ipv4.conf.lo.disable_policy = 1
net.ipv4.conf.lo.disable_xfrm = 1
net.ipv4.conf.lo.force_igmp_version = 0
net.ipv4.conf.lo.forwarding = 0
net.ipv4.conf.lo.igmpv2_unsolicited_report_interval = 10000
net.ipv4.conf.lo.igmpv3_unsolicited_report_interval = 1000
net.ipv4.conf.lo.log_martians = 0
net.ipv4.conf.lo.mc_forwarding = 0
net.ipv4.conf.lo.medium_id = 0
net.ipv4.conf.lo.promote_secondaries = 0
net.ipv4.conf.lo.proxy_arp = 0
net.ipv4.conf.lo.proxy_arp_pvlan = 0
net.ipv4.conf.lo.route_localnet = 0
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.lo.secure_redirects = 1
net.ipv4.conf.lo.send_redirects = 1
net.ipv4.conf.lo.shared_media = 1
net.ipv4.conf.lo.src_valid_mark = 0
net.ipv4.conf.lo.tag = 0
net.ipv4.conf.wlan0.accept_local = 0
net.ipv4.conf.wlan0.accept_redirects = 1
net.ipv4.conf.wlan0.accept_source_route = 1
net.ipv4.conf.wlan0.arp_accept = 0
net.ipv4.conf.wlan0.arp_announce = 0
net.ipv4.conf.wlan0.arp_filter = 0
net.ipv4.conf.wlan0.arp_ignore = 0
net.ipv4.conf.wlan0.arp_notify = 0
net.ipv4.conf.wlan0.bootp_relay = 0
net.ipv4.conf.wlan0.disable_policy = 0
net.ipv4.conf.wlan0.disable_xfrm = 0
net.ipv4.conf.wlan0.force_igmp_version = 0
net.ipv4.conf.wlan0.forwarding = 0
net.ipv4.conf.wlan0.igmpv2_unsolicited_report_interval = 10000
net.ipv4.conf.wlan0.igmpv3_unsolicited_report_interval = 1000
net.ipv4.conf.wlan0.log_martians = 0
net.ipv4.conf.wlan0.mc_forwarding = 0
net.ipv4.conf.wlan0.medium_id = 0
net.ipv4.conf.wlan0.promote_secondaries = 0
net.ipv4.conf.wlan0.proxy_arp = 0
net.ipv4.conf.wlan0.proxy_arp_pvlan = 0
net.ipv4.conf.wlan0.route_localnet = 0
net.ipv4.conf.wlan0.rp_filter = 1
net.ipv4.conf.wlan0.secure_redirects = 1
net.ipv4.conf.wlan0.send_redirects = 1
net.ipv4.conf.wlan0.shared_media = 1
net.ipv4.conf.wlan0.src_valid_mark = 0
net.ipv4.conf.wlan0.tag = 0
net.ipv4.icmp_echo_ignore_all = 0
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.icmp_errors_use_inbound_ifaddr = 0
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.icmp_ratelimit = 1000
net.ipv4.icmp_ratemask = 6168
net.ipv4.igmp_max_memberships = 20
net.ipv4.igmp_max_msf = 10
net.ipv4.inet_peer_maxttl = 600
net.ipv4.inet_peer_minttl = 120
net.ipv4.inet_peer_threshold = 65664
net.ipv4.ip_default_ttl = 64
net.ipv4.ip_dynaddr = 0
net.ipv4.ip_early_demux = 1
net.ipv4.ip_forward = 0
net.ipv4.ip_local_port_range = 32768 61000
net.ipv4.ip_local_reserved_ports =
net.ipv4.ip_no_pmtu_disc = 0
net.ipv4.ip_nonlocal_bind = 0
net.ipv4.ipfrag_high_thresh = 4194304
net.ipv4.ipfrag_low_thresh = 3145728
net.ipv4.ipfrag_max_dist = 64
net.ipv4.ipfrag_secret_interval = 600
net.ipv4.ipfrag_time = 30
net.ipv4.neigh.default.anycast_delay = 100
net.ipv4.neigh.default.app_solicit = 0
net.ipv4.neigh.default.base_reachable_time_ms = 30000
net.ipv4.neigh.default.delay_first_probe_time = 5
net.ipv4.neigh.default.gc_interval = 30
net.ipv4.neigh.default.gc_stale_time = 60
net.ipv4.neigh.default.gc_thresh1 = 128
net.ipv4.neigh.default.gc_thresh2 = 512
net.ipv4.neigh.default.gc_thresh3 = 1024
net.ipv4.neigh.default.locktime = 100
net.ipv4.neigh.default.mcast_solicit = 3
net.ipv4.neigh.default.proxy_delay = 80
net.ipv4.neigh.default.proxy_qlen = 64
net.ipv4.neigh.default.retrans_time_ms = 1000
net.ipv4.neigh.default.ucast_solicit = 3
net.ipv4.neigh.default.unres_qlen = 31
net.ipv4.neigh.default.unres_qlen_bytes = 65536
net.ipv4.neigh.lo.anycast_delay = 100
net.ipv4.neigh.lo.app_solicit = 0
net.ipv4.neigh.lo.base_reachable_time_ms = 30000
net.ipv4.neigh.lo.delay_first_probe_time = 5
net.ipv4.neigh.lo.gc_stale_time = 60
net.ipv4.neigh.lo.locktime = 100
net.ipv4.neigh.lo.mcast_solicit = 3
net.ipv4.neigh.lo.proxy_delay = 80
net.ipv4.neigh.lo.proxy_qlen = 64
net.ipv4.neigh.lo.retrans_time_ms = 1000
net.ipv4.neigh.lo.ucast_solicit = 3
net.ipv4.neigh.lo.unres_qlen = 31
net.ipv4.neigh.lo.unres_qlen_bytes = 65536
net.ipv4.neigh.wlan0.anycast_delay = 100
net.ipv4.neigh.wlan0.app_solicit = 0
net.ipv4.neigh.wlan0.base_reachable_time_ms = 30000
net.ipv4.neigh.wlan0.delay_first_probe_time = 5
net.ipv4.neigh.wlan0.gc_stale_time = 60
net.ipv4.neigh.wlan0.locktime = 100
net.ipv4.neigh.wlan0.mcast_solicit = 3
net.ipv4.neigh.wlan0.proxy_delay = 80
net.ipv4.neigh.wlan0.proxy_qlen = 64
net.ipv4.neigh.wlan0.retrans_time_ms = 1000
net.ipv4.neigh.wlan0.ucast_solicit = 3
net.ipv4.neigh.wlan0.unres_qlen = 31
net.ipv4.neigh.wlan0.unres_qlen_bytes = 65536
net.ipv4.ping_group_range = 1 0
net.ipv4.route.error_burst = 1250
net.ipv4.route.error_cost = 250
net.ipv4.route.gc_elasticity = 8
net.ipv4.route.gc_interval = 60
net.ipv4.route.gc_min_interval = 0
net.ipv4.route.gc_min_interval_ms = 500
net.ipv4.route.gc_thresh = -1
net.ipv4.route.gc_timeout = 300
net.ipv4.route.max_size = 2147483647
net.ipv4.route.min_adv_mss = 256
net.ipv4.route.min_pmtu = 552
net.ipv4.route.mtu_expires = 600
net.ipv4.route.redirect_load = 5
net.ipv4.route.redirect_number = 9
net.ipv4.route.redirect_silence = 5120
net.ipv4.tcp_abort_on_overflow = 0
net.ipv4.tcp_adv_win_scale = 1
net.ipv4.tcp_allowed_congestion_control = cubic reno
net.ipv4.tcp_app_win = 31
net.ipv4.tcp_available_congestion_control = cubic reno
net.ipv4.tcp_base_mss = 512
net.ipv4.tcp_challenge_ack_limit = 100
net.ipv4.tcp_congestion_control = cubic
net.ipv4.tcp_dsack = 1
net.ipv4.tcp_early_retrans = 3
net.ipv4.tcp_ecn = 2
net.ipv4.tcp_fack = 1
net.ipv4.tcp_fastopen = 1
net.ipv4.tcp_fastopen_key = 00000000-00000000-00000000-00000000
net.ipv4.tcp_fin_timeout = 60
net.ipv4.tcp_frto = 2
net.ipv4.tcp_keepalive_intvl = 75
net.ipv4.tcp_keepalive_probes = 9
net.ipv4.tcp_keepalive_time = 7200
net.ipv4.tcp_limit_output_bytes = 131072
net.ipv4.tcp_low_latency = 0
net.ipv4.tcp_max_orphans = 32768
net.ipv4.tcp_max_syn_backlog = 256
net.ipv4.tcp_max_tw_buckets = 32768
net.ipv4.tcp_mem = 189114 252152 378228
net.ipv4.tcp_min_tso_segs = 2
net.ipv4.tcp_moderate_rcvbuf = 1
net.ipv4.tcp_mtu_probing = 0
net.ipv4.tcp_no_metrics_save = 0
net.ipv4.tcp_notsent_lowat = -1
net.ipv4.tcp_orphan_retries = 0
net.ipv4.tcp_reordering = 3
net.ipv4.tcp_retrans_collapse = 1
net.ipv4.tcp_retries1 = 3
net.ipv4.tcp_retries2 = 15
net.ipv4.tcp_rfc1337 = 0
net.ipv4.tcp_rmem = 4096 87380 6291456
net.ipv4.tcp_sack = 1
net.ipv4.tcp_slow_start_after_idle = 1
net.ipv4.tcp_stdurg = 0
net.ipv4.tcp_syn_retries = 6
net.ipv4.tcp_synack_retries = 5
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_thin_dupack = 0
net.ipv4.tcp_thin_linear_timeouts = 0
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_tso_win_divisor = 3
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_tw_reuse = 0
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_wmem = 4096 16384 4194304
net.ipv4.tcp_workaround_signed_windows = 0
net.ipv4.udp_mem = 189114 252152 378228
net.ipv4.udp_rmem_min = 4096
net.ipv4.udp_wmem_min = 4096
net.ipv4.xfrm4_gc_thresh = 32768
net.ipv6.bindv6only = 0
net.ipv6.conf.all.accept_dad = 1
net.ipv6.conf.all.accept_ra = 1
net.ipv6.conf.all.accept_ra_defrtr = 1
net.ipv6.conf.all.accept_ra_pinfo = 1
net.ipv6.conf.all.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.all.accept_ra_rtr_pref = 1
net.ipv6.conf.all.accept_redirects = 1
net.ipv6.conf.all.accept_source_route = 0
net.ipv6.conf.all.autoconf = 1
net.ipv6.conf.all.dad_transmits = 1
net.ipv6.conf.all.disable_ipv6 = 0
net.ipv6.conf.all.force_mld_version = 0
net.ipv6.conf.all.force_tllao = 0
net.ipv6.conf.all.forwarding = 0
net.ipv6.conf.all.hop_limit = 64
net.ipv6.conf.all.max_addresses = 16
net.ipv6.conf.all.max_desync_factor = 600
net.ipv6.conf.all.mc_forwarding = 0
net.ipv6.conf.all.mldv1_unsolicited_report_interval = 10000
net.ipv6.conf.all.mldv2_unsolicited_report_interval = 1000
net.ipv6.conf.all.mtu = 1280
net.ipv6.conf.all.ndisc_notify = 0
net.ipv6.conf.all.proxy_ndp = 0
net.ipv6.conf.all.regen_max_retry = 3
net.ipv6.conf.all.router_probe_interval = 60
net.ipv6.conf.all.router_solicitation_delay = 1
net.ipv6.conf.all.router_solicitation_interval = 4
net.ipv6.conf.all.router_solicitations = 3
net.ipv6.conf.all.suppress_frag_ndisc = 1
net.ipv6.conf.all.temp_prefered_lft = 86400
net.ipv6.conf.all.temp_valid_lft = 604800
net.ipv6.conf.all.use_tempaddr = 2
net.ipv6.conf.default.accept_dad = 1
net.ipv6.conf.default.accept_ra = 1
net.ipv6.conf.default.accept_ra_defrtr = 1
net.ipv6.conf.default.accept_ra_pinfo = 1
net.ipv6.conf.default.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.default.accept_ra_rtr_pref = 1
net.ipv6.conf.default.accept_redirects = 1
net.ipv6.conf.default.accept_source_route = 0
net.ipv6.conf.default.autoconf = 1
net.ipv6.conf.default.dad_transmits = 1
net.ipv6.conf.default.disable_ipv6 = 0
net.ipv6.conf.default.force_mld_version = 0
net.ipv6.conf.default.force_tllao = 0
net.ipv6.conf.default.forwarding = 0
net.ipv6.conf.default.hop_limit = 64
net.ipv6.conf.default.max_addresses = 16
net.ipv6.conf.default.max_desync_factor = 600
net.ipv6.conf.default.mc_forwarding = 0
net.ipv6.conf.default.mldv1_unsolicited_report_interval = 10000
net.ipv6.conf.default.mldv2_unsolicited_report_interval = 1000
net.ipv6.conf.default.mtu = 1280
net.ipv6.conf.default.ndisc_notify = 0
net.ipv6.conf.default.proxy_ndp = 0
net.ipv6.conf.default.regen_max_retry = 3
net.ipv6.conf.default.router_probe_interval = 60
net.ipv6.conf.default.router_solicitation_delay = 1
net.ipv6.conf.default.router_solicitation_interval = 4
net.ipv6.conf.default.router_solicitations = 3
net.ipv6.conf.default.suppress_frag_ndisc = 1
net.ipv6.conf.default.temp_prefered_lft = 86400
net.ipv6.conf.default.temp_valid_lft = 604800
net.ipv6.conf.default.use_tempaddr = 2
net.ipv6.conf.lo.accept_dad = -1
net.ipv6.conf.lo.accept_ra = 1
net.ipv6.conf.lo.accept_ra_defrtr = 1
net.ipv6.conf.lo.accept_ra_pinfo = 1
net.ipv6.conf.lo.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.lo.accept_ra_rtr_pref = 1
net.ipv6.conf.lo.accept_redirects = 1
net.ipv6.conf.lo.accept_source_route = 0
net.ipv6.conf.lo.autoconf = 1
net.ipv6.conf.lo.dad_transmits = 1
net.ipv6.conf.lo.disable_ipv6 = 0
net.ipv6.conf.lo.force_mld_version = 0
net.ipv6.conf.lo.force_tllao = 0
net.ipv6.conf.lo.forwarding = 0
net.ipv6.conf.lo.hop_limit = 64
net.ipv6.conf.lo.max_addresses = 16
net.ipv6.conf.lo.max_desync_factor = 600
net.ipv6.conf.lo.mc_forwarding = 0
net.ipv6.conf.lo.mldv1_unsolicited_report_interval = 10000
net.ipv6.conf.lo.mldv2_unsolicited_report_interval = 1000
net.ipv6.conf.lo.mtu = 65536
net.ipv6.conf.lo.ndisc_notify = 0
net.ipv6.conf.lo.proxy_ndp = 0
net.ipv6.conf.lo.regen_max_retry = 3
net.ipv6.conf.lo.router_probe_interval = 60
net.ipv6.conf.lo.router_solicitation_delay = 1
net.ipv6.conf.lo.router_solicitation_interval = 4
net.ipv6.conf.lo.router_solicitations = 3
net.ipv6.conf.lo.suppress_frag_ndisc = 1
net.ipv6.conf.lo.temp_prefered_lft = 86400
net.ipv6.conf.lo.temp_valid_lft = 604800
net.ipv6.conf.lo.use_tempaddr = 2
net.ipv6.conf.wlan0.accept_dad = 1
net.ipv6.conf.wlan0.accept_ra = 2
net.ipv6.conf.wlan0.accept_ra_defrtr = 1
net.ipv6.conf.wlan0.accept_ra_pinfo = 1
net.ipv6.conf.wlan0.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.wlan0.accept_ra_rtr_pref = 1
net.ipv6.conf.wlan0.accept_redirects = 1
net.ipv6.conf.wlan0.accept_source_route = 0
net.ipv6.conf.wlan0.autoconf = 1
net.ipv6.conf.wlan0.dad_transmits = 1
net.ipv6.conf.wlan0.disable_ipv6 = 0
net.ipv6.conf.wlan0.force_mld_version = 0
net.ipv6.conf.wlan0.force_tllao = 0
net.ipv6.conf.wlan0.forwarding = 0
net.ipv6.conf.wlan0.hop_limit = 64
net.ipv6.conf.wlan0.max_addresses = 16
net.ipv6.conf.wlan0.max_desync_factor = 600
net.ipv6.conf.wlan0.mc_forwarding = 0
net.ipv6.conf.wlan0.mldv1_unsolicited_report_interval = 10000
net.ipv6.conf.wlan0.mldv2_unsolicited_report_interval = 1000
net.ipv6.conf.wlan0.mtu = 1500
net.ipv6.conf.wlan0.ndisc_notify = 0
net.ipv6.conf.wlan0.proxy_ndp = 0
net.ipv6.conf.wlan0.regen_max_retry = 3
net.ipv6.conf.wlan0.router_probe_interval = 60
net.ipv6.conf.wlan0.router_solicitation_delay = 1
net.ipv6.conf.wlan0.router_solicitation_interval = 4
net.ipv6.conf.wlan0.router_solicitations = 3
net.ipv6.conf.wlan0.suppress_frag_ndisc = 1
net.ipv6.conf.wlan0.temp_prefered_lft = 86400
net.ipv6.conf.wlan0.temp_valid_lft = 604800
net.ipv6.conf.wlan0.use_tempaddr = 2
net.ipv6.icmp.ratelimit = 1000
net.ipv6.ip6frag_high_thresh = 4194304
net.ipv6.ip6frag_low_thresh = 3145728
net.ipv6.ip6frag_secret_interval = 600
net.ipv6.ip6frag_time = 60
net.ipv6.mld_max_msf = 64
net.ipv6.neigh.default.anycast_delay = 100
net.ipv6.neigh.default.app_solicit = 0
net.ipv6.neigh.default.base_reachable_time_ms = 30000
net.ipv6.neigh.default.delay_first_probe_time = 5
net.ipv6.neigh.default.gc_interval = 30
net.ipv6.neigh.default.gc_stale_time = 60
net.ipv6.neigh.default.gc_thresh1 = 128
net.ipv6.neigh.default.gc_thresh2 = 512
net.ipv6.neigh.default.gc_thresh3 = 1024
net.ipv6.neigh.default.locktime = 0
net.ipv6.neigh.default.mcast_solicit = 3
net.ipv6.neigh.default.proxy_delay = 80
net.ipv6.neigh.default.proxy_qlen = 64
net.ipv6.neigh.default.retrans_time_ms = 1000
net.ipv6.neigh.default.ucast_solicit = 3
net.ipv6.neigh.default.unres_qlen = 31
net.ipv6.neigh.default.unres_qlen_bytes = 65536
net.ipv6.neigh.lo.anycast_delay = 100
net.ipv6.neigh.lo.app_solicit = 0
net.ipv6.neigh.lo.base_reachable_time_ms = 30000
net.ipv6.neigh.lo.delay_first_probe_time = 5
net.ipv6.neigh.lo.gc_stale_time = 60
net.ipv6.neigh.lo.locktime = 0
net.ipv6.neigh.lo.mcast_solicit = 3
net.ipv6.neigh.lo.proxy_delay = 80
net.ipv6.neigh.lo.proxy_qlen = 64
net.ipv6.neigh.lo.retrans_time_ms = 1000
net.ipv6.neigh.lo.ucast_solicit = 3
net.ipv6.neigh.lo.unres_qlen = 31
net.ipv6.neigh.lo.unres_qlen_bytes = 65536
net.ipv6.neigh.wlan0.anycast_delay = 100
net.ipv6.neigh.wlan0.app_solicit = 0
net.ipv6.neigh.wlan0.base_reachable_time_ms = 30000
net.ipv6.neigh.wlan0.delay_first_probe_time = 5
net.ipv6.neigh.wlan0.gc_stale_time = 60
net.ipv6.neigh.wlan0.locktime = 0
net.ipv6.neigh.wlan0.mcast_solicit = 3
net.ipv6.neigh.wlan0.proxy_delay = 80
net.ipv6.neigh.wlan0.proxy_qlen = 64
net.ipv6.neigh.wlan0.retrans_time_ms = 1000
net.ipv6.neigh.wlan0.ucast_solicit = 3
net.ipv6.neigh.wlan0.unres_qlen = 31
net.ipv6.neigh.wlan0.unres_qlen_bytes = 65536
net.ipv6.route.gc_elasticity = 9
net.ipv6.route.gc_interval = 30
net.ipv6.route.gc_min_interval = 0
net.ipv6.route.gc_min_interval_ms = 500
net.ipv6.route.gc_thresh = 1024
net.ipv6.route.gc_timeout = 60
net.ipv6.route.max_size = 4096
net.ipv6.route.min_adv_mss = 1220
net.ipv6.route.mtu_expires = 600
net.ipv6.xfrm6_gc_thresh = 32768
net.netfilter.nf_log.0 = NONE
net.netfilter.nf_log.1 = NONE
net.netfilter.nf_log.10 = NONE
net.netfilter.nf_log.11 = NONE
net.netfilter.nf_log.12 = NONE
net.netfilter.nf_log.2 = NONE
net.netfilter.nf_log.3 = NONE
net.netfilter.nf_log.4 = NONE
net.netfilter.nf_log.5 = NONE
net.netfilter.nf_log.6 = NONE
net.netfilter.nf_log.7 = NONE
net.netfilter.nf_log.8 = NONE
net.netfilter.nf_log.9 = NONE
net.unix.max_dgram_qlen = 10

[nikkoara]

That's strange. Could you give us more details on the system environment?

I have tested my findings on another Linux box (a Slackware 14.1) where I have noticed the slowdown, albeit less severe. E.g., it takes a 20M DICOM between 1s and 11s to transfer. I have verified that explicitly setting the TCP_BUFFER_LENGTH envar to a large value, e.g., 20K, 64K, 150K, etc. speeds up the transfer.

After ifdef'ing out setTcpBufferLength function body the transfer is consistently taking place in as little as 1/10s (I used time to collect storescu execution time).

Back to the original Ubuntu box. I have collected net stats with 'netstat -s' and they showed that slow transfers were invariably accompanied by a reduced (or zero) number of predicted acknowledgments (TCPHPAcks). The occasional runs which were faster showed a proportionally larger number of TCPHPAcks. A cursory look into kernel's tcp_input.c shows that this MIB counter is updated in one branch of an if conditional in function tcp_ack. The other branch updates the receive window.

FWIW I am thinking about ditching setTcpBufferLength in our builds, and removing the disabling of the Nagle algorithm as well. According to Stevens, the former should happen before connect for clients and before listen for servers, anyway. The latter we discovered by accident during this investigation and we found it odd that it is the default.

[J. Riesmeier]

Thank you for your detailed analysis. These parts of the network code are rather old. Maybe, we should recheck whether they are still useful. Assessing the pros and cons of the Nagle algorithm on modern operating systems is already on our to-do list. I will also add the TCP buffer question to it.

[nikkoara]

Thank you for your detailed analysis. These parts of the network code are rather old. Maybe, we should recheck whether they are still useful. Assessing the pros and cons of the Nagle algorithm on modern operating systems is already on our to-do list. I will also add the TCP buffer question to it.

I am happy to help in any way I can. We are greatly benefiting from this project.

[tpalagyi]

FYI, I am experiencing the same problem with the git trunk version. Unfortunately I found this topic after my own struggle that I described in http://lapraszerelt.blogspot.hu/2016/02 ... -slow.html .

[J. Riesmeier]

This issue has been fixed with commit 8df1f5e. See commit message for details.

Also the the Nagle algorithm is not disabled anymore (at least not by default, the user can decide). See commit ffecd24.