When not resetting t_nom, negative credit never clears
Here is a log which I took after dropping the 3d patch which resets t_nom when tnom < t_now. It shows that the negative credit does not clear, hence all packets are sent in one huge burst.
[ 75.646215] ccid3_hc_tx_update_x: X_prev#743226, X_now#728510, X_calc=0, X_recv864255 [ 75.646218] ccid3_update_send_interval: t_ipiY, delta), s15, X#728510 [ 75.646223] ccid3_hc_tx_packet_recv: client(f651c080), RTTD98us (sampleU17us), s15, p=0, X_calc=0, X_recv864255, X#728510 [ 75.646264] ccid3_hc_tx_send_packet: delay=-14235 [ 75.646314] ccid3_hc_tx_send_packet: delay=-14226 [ 75.646451] ccid3_hc_tx_send_packet: delay=-14304 [ 75.646454] ccid3_hc_tx_update_win_count: now at 0X3 [ 75.646548] ccid3_hc_tx_send_packet: delay=-14343 [ 75.646759] ccid3_hc_tx_send_packet: delay=-14494 [ 75.646802] ccid3_hc_tx_send_packet: delay=-14479 [ 75.646923] ccid3_hc_tx_send_packet: delay=-14541 [ 75.647045] ccid3_hc_tx_send_packet: delay=-14604 [ 75.647205] ccid3_hc_tx_send_packet: delay=-14705 [ 75.647266] ccid3_hc_tx_send_packet: delay=-14707 [ 75.647384] ccid3_hc_tx_send_packet: delay=-14767 [ 75.647564] ccid3_hc_tx_send_packet: delay=-14888 [ 75.647623] ccid3_hc_tx_send_packet: delay=-14888 [ 75.647627] ccid3_hc_tx_update_win_count: now at 0X4 [ 75.647812] ccid3_hc_tx_send_packet: delay=-15018 [ 75.647907] ccid3_hc_tx_send_packet: delay=-15055 [ 75.647984] ccid3_hc_tx_send_packet: delay=-15072 [ 75.648114] ccid3_hc_tx_send_packet: delay=-15144 [ 75.648223] ccid3_hc_tx_send_packet: delay=-15194 [ 75.648373] ccid3_hc_tx_send_packet: delay=-15285 [ 75.648526] ccid3_hc_tx_send_packet: delay=-15380 [ 75.648657] ccid3_hc_tx_send_packet: delay=-15452 [ 75.648706] ccid3_hc_tx_send_packet: delay=-15442 [ 75.648820] ccid3_hc_tx_send_packet: delay=-15498 [ 75.648824] ccid3_hc_tx_update_win_count: now at 0X5 [ 75.649013] ccid3_hc_tx_send_packet: delay=-15631 [ 75.649060] ccid3_hc_tx_send_packet: delay=-15620 [ 75.649223] ccid3_hc_tx_send_packet: delay=-15724 [ 75.649333] ccid3_hc_tx_send_packet: delay=-15775 [ 75.649419] ccid3_hc_tx_send_packet: delay=-15802 [ 75.649537] ccid3_hc_tx_send_packet: delay=-15862 [ 75.649657] ccid3_hc_tx_send_packet: delay=-15922 [ 75.649788] ccid3_hc_tx_send_packet: delay=-15995 [ 75.649934] ccid3_hc_tx_send_packet: delay=-16082 [ 75.650066] ccid3_hc_tx_send_packet: delay=-16155 [ 75.650069] ccid3_hc_tx_update_win_count: now at 0X6 [ 75.650137] ccid3_hc_tx_send_packet: delay=-16167 [ 75.650256] ccid3_hc_tx_send_packet: delay=-16228 [ 75.650442] ccid3_hc_tx_send_packet: delay=-16355 [ 75.650499] ccid3_hc_tx_send_packet: delay=-16353 [ 75.650666] ccid3_hc_tx_send_packet: delay=-16461 [ 75.650771] ccid3_hc_tx_send_packet: delay=-16508 [ 75.650855] ccid3_hc_tx_send_packet: delay=-16533 [ 75.650974] ccid3_hc_tx_send_packet: delay=-16593 [ 75.651076] dccp_v4_rcv: ACK src9.133.209.65@5001 dst9.133.209.75@33438 seq4797824647, ack 51983126 [ 75.651086] ccid3_hc_tx_parse_options: client(f651c080), RECEIVE_RATE876322 [ 75.651090] ccid3_hc_tx_parse_options: client(f651c080), LOSS_EVENT_RATEB94967295 [ 75.651094] dccp_parse_options: client rx opt: TIMESTAMP3608, ackno 51983126 [ 75.651098] dccp_parse_options: client rx opt: NDP countG [ 75.651103] ccid3_hc_tx_update_x: X_prev#728510, X_now#752644, X_calc=0, X_recv876322 [ 75.651107] ccid3_update_send_interval: t_ipiY, delta), s15, X#752644 [ 75.651112] ccid3_hc_tx_packe.748504] ccid3_hc_tx_send_packet: delay=-66203 [ 75.748624] ccid3_hc_tx_send_packet: delay=-66264 [ 75.748836] ccid3_hc_tx_send_packet: delay=-66418 [ 75.748880] ccid3_hc_tx_send_packet: delay=-66403 [ 75.749011] ccid3_hc_tx_send_packet: delay=-66474 [ 75.749159] ccid3_hc_tx_send_packet: delay=-66563 [ 75.749222] ccid3_hc_tx_send_packet: delay=-66568 [ 75.749340] ccid3_hc_tx_send_packet: delay=-66627 [ 75.749344] ccid3_hc_tx_update_win_count: now at 0X0 [ 75.749527] ccid3_hc_tx_send_packet: delay=-66755 [ 75.749586] ccid3_hc_tx_send_packet: delay=-66756 [ 75.749757] ccid3_hc_tx_send_packet: delay=-66867 [ 75.749820] ccid3_hc_tx_send_packet: delay=-66872 [ 75.749936] ccid3_hc_tx_send_packet: delay=-66929 [ 75.750056] ccid3_hc_tx_send_packet: delay=-66990 [ 75.750175] ccid3_hc_tx_send_packet: delay=-67051 [ 75.750298] ccid3_hc_tx_send_packet: delay=-67114 [ 75.750423] ccid3_hc_tx_send_packet: delay=-67180 [ 75.750540] ccid3_hc_tx_send_packet: delay=-67239 [ 75.750657] dccp_v4_rcv: ACK src9.133.209.65@5001 dst9.133.209.75@33438 seq4797824666, ack 51983958 [ 75.750666] ccid3_hc_tx_parse_options: client(f651c080), RECEIVE_RATE948536 [ 75.750670] ccid3_hc_tx_parse_options: client(f651c080), LOSS_EVENT_RATEB94967295 [ 75.750674] dccp_parse_options: client rx opt: TIMESTAMP3580, ackno 51983958 [ 75.750677] dccp_parse_options: client rx opt: NDP countf [ 75.750682] ccid3_hc_tx_update_x: X_prev#637034, X_now#897072, X_calc=0, X_recv948536 [ 75.750686] ccid3_update_send_interval: t_ipiY, delta), s15, X#897072 [ 75.750691] ccid3_hc_tx_packet_recv: client(f651c080), RTTS41us (sampleT63us), s15, p=0, X_calc=0, X_recv948536, X#897072 [ 75.750740] ccid3_hc_tx_send_packet: delay=-67380 [ 75.750746] ccid3_hc_tx_update_win_count: now at 0X1 [ 75.750795] ccid3_hc_tx_send_packet: delay=-67377 [ 75.750950] ccid3_hc_tx_send_packet: delay=-67473 [ 75.751017] ccid3_hc_tx_send_packet: delay=-67481 [ 75.751134] ccid3_hc_tx_send_packet: delay=-67539 [ 75.751248] ccid3_hc_tx_send_packet: delay=-67595 [ 75.751372] ccid3_hc_tx_send_packet: delay=-67660 [ 75.751514] ccid3_hc_tx_send_packet: delay=-67743 [ 75.751612] ccid3_hc_tx_send_packet: delay=-67782 [ 75.751850] ccid3_hc_tx_send_packet: delay=-67961 [ 75.751885] ccid3_hc_tx_send_packet: delay=-67938 [ 75.751971] ccid3_hc_tx_send_packet: delay=-67964 [ 75.752130] ccid3_hc_tx_send_packet: delay=-68065 [ 75.752134] ccid3_hc_tx_update_win_count: now at 0X2 [ 75.752242] ccid3_hc_tx_send_packet: delay=-68118 [ 75.752334] ccid3_hc_tx_send_packet: delay=-68151 [ 75.752452] ccid3_hc_tx_send_packet: delay=-68210 [ 75.752664] ccid3_hc_tx_send_packet: delay=-68363 [ 75.752706] ccid3_hc_tx_send_packet: delay=-68347 [ 75.752809] ccid3_hc_tx_send_packet: delay=-68391 [ 75.752928] ccid3_hc_tx_send_packet: delay=-68451 [ 75.753057] ccid3_hc_tx_send_packet: delay=-68521 [ 75.753167] ccid3_hc_tx_send_packet: delay=-68573 [ 75.753287] ccid3_hc_tx_send_packet: delay=-68634 [ 75.753420] ccid3_hc_tx_send_packet: delay=-68707 [ 75.753526] ccid3_hc_tx_send_packet: delay=-68755 [ 75.753529] ccid3_hc_tx_update_win_count: now at 0X3 [ 75.753646] ccid3_hc_tx_send_packet: delay=-68817 [ 75.753774] ccid3_hc_tx_send_packet: delay=-68886 [ 75.753885] ccid3_hc_tx_send_packet: delay=-68937 [ 75.754005] ccid3_hc_tx_send_packet: delay=-68998 [ 75.754168] ccid3_hc_tx_send_packet: delay=-69103 [ 75.754245] ccid3_hc_tx_send_packet: delay=-69121 [ 75.754434] ccid3_hc_tx_send_packet: delay=-69251 [ 75.754492] ccid3_hc_tx_send_packet: delay=-69250 [ 75.754607] ccid3_hc_tx_send_packet: delay=-69307 [ 75.754738] ccid3_hc_tx_send_packet: delay=-69d3_hc_tx_update_win_count: now at 0X3 [ 75.867811] ccid3_hc_tx_send_packet: delay=-126884 [ 75.867972] ccid3_hc_tx_send_packet: delay=-126987 [ 75.868076] ccid3_hc_tx_send_packet: delay=-127032 [ 75.868170] ccid3_hc_tx_send_packet: delay=-127067 [ 75.868290] ccid3_hc_tx_send_packet: delay=-127129 [ 75.868497] ccid3_hc_tx_send_packet: delay=-127277 [ 75.868539] ccid3_hc_tx_send_packet: delay=-127260 [ 75.868686] dccp_v4_rcv: ACK src9.133.209.65@5001 dst9.133.209.75@33438 seq4797824688, ack 51984944 [ 75.868695] ccid3_hc_tx_parse_options: client(f651c080), RECEIVE_RATE879866 [ 75.868699] ccid3_hc_tx_parse_options: c_recv879866 [ 75.868714] ccid3_update_send_interval: t_ipiY, delta), s15, X#759732 [ 75.868719] ccid3_hc_tx_packet_recv: client(f651c080), RTTT31us (sampleT71us), s15, p=0, X_calc=0, X_recv879866, X#759732 [ 75.868748] ccid3_hc_tx_send_packet: delay=-127411 [ 75.868859] ccid3_hc_tx_send_packet: delay=-127463 [ 75.868983] ccid3_hc_tx_send_packet: delay=-127527 [ 75.869028] ccid3_hc_tx_send_packet: delay=-127513 [ 75.869212] ccid3_hc_tx_send_packet: delay=-127639 [ 75.869215] ccid3_hc_tx_update_win_count: now at 0X4 [ 75.869261] ccid3_hc_tx_send_packet: delay=-127627 [ 75.869435] ccid3_hc_tx_send_packet: delay=-127744 [ 75.869533] ccid3_hc_tx_send_packet: delay=-127783 [ 75.869607] ccid3_hc_tx_send_packet: delay=-127799 [ 75.869735] ccid3_hc_tx_send_packet: delay=-127868 [ 75.869847] ccid3_hc_tx_send_packet: delay=-127921 [ 75.870051] ccid3_hc_tx_send_packet: delay=-128066 [ 75.870092] ccid3_hc_tx_send_packet: delay=-128049 [ 75.870238] ccid3_hc_tx_send_packet: delay=-128135 [ 75.870385] ccid3_hc_tx_send_packet: delay=-128223 [ 75.870446] ccid3_hc_tx_send_packet: delay=-128226 [ 75.870564] ccid3_hc_tx_send_packet: delay=-128285 [ 75.870834] ccid3_hc_tx_send_packet: delay=-128496 [ 75.870837] ccid3_hc_tx_update_win_count: now at 0X5 [ 75.870872] ccid3_hc_tx_send_packet: delay=-128476 [ 75.870926] ccid3_hc_tx_send_packet: delay=-128471 [ 75.871108] ccid3_hc_tx_send_packet: delay=-128594 [ 75.871165] ccid3_hc_tx_send_packet: delay=-128592 [ 75.871278] ccid3_hc_tx_send_packet: delay=-128646 [ 75.871399] ccid3_hc_tx_send_packet: delay=-128708 [ 75.871518] ccid3_hc_tx_send_packet: delay=-128769 [ 75.871637] ccid3_hc_tx_send_packet: delay=-128829 [ 75.871758] ccid3_hc_tx_send_packet: delay=-128891 [ 75.871880] ccid3_hc_tx_send_packet: delay=-128954 [ 75.872004] ccid3_hc_tx_send_packet: delay=-129019 [ 75.872120] ccid3_hc_tx_send_packet: delay=-129077 [ 75.872272] ccid3_hc_tx_send_packet: delay=-129170 [ 75.872276] ccid3_hc_tx_update_win_count: now at 0X6 [ 75.872356] ccid3_hc_tx_send_packet: delay=-129195 [ 75.872543] ccid3_hc_tx_send_packet: delay=-129323 [ 75.872601] ccid3_hc_tx_send_packet: delay=-129322 [ 75.872781] ccid3_hc_tx_send_packet: delay=-129444 [ 75.872839] ccid3_hc_tx_send_packet: delay=-129443 [ 75.872954] ccid3_hc_tx_send_packet: delay=-129499 [ 75.873079] ccid3_hc_tx_send_packet: delay=-129565 [ 75.873321] ccid3_hc_tx_send_packet: delay=-129749 [ 75.873355] ccid3_hc_tx_send_packet: delay=-129724 [ 75.873528] ccid3_hc_tx_send_packet: delay=-129838 [ 75.873601] ccid3_hc_tx_send_packet: delay=-129851 [ 75.873675] ccid3_hc_tx_send_packet: delay=-129867 [ 75.873679] ccid3_hc_tx_update_win_count: now at 0X7 [ 75.873819] ccid3_hc_tx_send_packet: delay=-129952 [ 75.873917] ccid3_hc_tx_send_packet: delay=-129991 [ 75.874005] dccp_v4_rcv: ACK src9.133.209.65@5001 dst9.133.209.75@33438 seq4797824689, ack 51984989 [ 75.874015] ccid3_hc_tx_parse_options: client(f651c080), RECEIVE_RATE879866 [ 75.874019] ccid3_hc_t ccid3_hc_tx_send_packet: delay=-182027 [ 75.976478] ccid3_hc_tx_send_packet: delay=-182070 [ 75.976590] ccid3_hc_tx_send_packet: delay=-182124 [ 75.976709] ccid3_hc_tx_send_packet: delay=-182184 [ 75.976907] ccid3_hc_tx_send_packet: delay=-182323 [ 75.976954] ccid3_hc_tx_send_packet: delay=-182311 [ 75.977082] ccid3_hc_tx_send_packet: delay=-182380 [ 75.977252] ccid3_hc_tx_send_packet: delay=-182491 [ 75.977310] ccid3_hc_tx_send_packet: delay=-182490 [ 75.977440] ccid3_hc_tx_send_packet: delay=-182562 [ 75.977619] ccid3_hc_tx_send_packet: delay=-182681 [ 75.977622] ccid3_hc_tx_update_win_count: now at 0X0 [ 75.977669] ccid3_hc_tx_send_packet: delay=-182673 [ 75.977833] ccid3_hc_tx_send_packet: delay=-182778 [ 75.977942] ccid3_hc_tx_send_packet: delay=-182828 [ 75.978032] ccid3_hc_tx_send_packet: delay=-182859 [ 75.978145] ccid3_hc_tx_send_packet: delay=-182914 [ 75.978265] ccid3_hc_tx_send_packet: delay=-182975 [ 75.978396] ccid3_hc_tx_send_packet: delay=-183048 [ 75.978549] ccid3_hc_tx_send_packet: delay=-183141 [ 75.978690] ccid3_hc_tx_send_packet: delay=-183223 [ 75.978748] ccid3_hc_tx_send_packet: delay=-183223 [ 75.978863] ccid3_hc_tx_send_packet: delay=-183279 [ 75.979098] ccid3_hc_tx_send_packet: delay=-183455 [ 75.979102] ccid3_hc_tx_update_win_count: now at 0X1 [ 75.979139] ccid3_hc_tx_send_packet: delay=-183435 [ 75.979304] ccid3_hc_tx_send_packet: delay=-183544 [ 75.979349] ccid3_hc_tx_send_packet: delay=-183530 [ 75.979457] ccid3_hc_tx_send_packet: delay=-183579 [ 75.979601] ccid3_hc_tx_send_packet: delay=-183664 [ 75.979701] ccid3_hc_tx_send_packet: delay=-183705 [ 75.979881] ccid3_hc_tx_send_packet: delay=-183827 [ 75.979941] ccid3_hc_tx_send_packet: delay=-183828 [ 75.980067] ccid3_hc_tx_send_packet: delay=-183895 [ 75.980219] ccid3_hc_tx_send_packet: delay=-183988 [ 75.980308] dccp_v4_rcv: ACK src9.133.209.65@5001 dst9.133.209.75@33438 seq4797824709, ack 51985877 [ 75.980316] ccid3_hc_tx_parse_options: client(f651c080), RECEIVE_RATE784088 [ 75.980320] ccid3_hc_tx_parse_options: client(f651c080), LOSS_EVENT_RATEB94967295 [ 75.980324] dccp_parse_options: client rx opt: TIMESTAMP6585, ackno 51985877 [ 75.980327] dccp_parse_options: client rx opt: NDP count9 [ 75.980333] ccid3_hc_tx_packet_recv: client(f651c080), RTTS80us (sampleT83us), s15, p=0, X_calc=0, X_recv784088, X#839284 [ 75.980436] ccid3_hc_tx_send_packet: delay=-184147 [ 75.980471] ccid3_hc_tx_send_packet: delay=-184123 [ 75.980477] ccid3_hc_tx_update_win_count: now at 0X2 [ 75.980671] ccid3_hc_tx_send_packet: delay=-184263 [ 75.980710] ccid3_hc_tx_send_packet: delay=-184241 [ 75.980779] ccid3_hc_tx_send_packet: delay=-184254 [ 75.980945] ccid3_hc_tx_send_packet: delay=-184361 [ 75.981063] ccid3_hc_tx_send_packet: delay=-184421 [ 75.981138] ccid3_hc_tx_send_packet: delay=-184436 [ 75.981257] ccid3_hc_tx_send_packet: delay=-184497 [ 75.981378] ccid3_hc_tx_send_packet: delay=-184559 [ 75.981527] ccid3_hc_tx_send_packet: delay=-184650 [ 75.981662] ccid3_hc_tx_send_packet: delay=-184726 [ 75.981734] ccid3_hc_tx_send_packet: delay=-184739 [ 75.981860] ccid3_hc_tx_send_packet: delay=-184805 [ 75.981863] ccid3_hc_tx_update_win_count: now at 0X3 [ 75.981992] ccid3_hc_tx_send_packet: delay=-184879 [ 75.982208] ccid3_hc_tx_send_packet: delay=-185036 [ 75.982246] ccid3_hc_tx_send_packet: delay=-185013 [ 75.982425] ccid3_hc_tx_send_packet: delay=-185136 [ 75.982472] ccid3_hc_tx_send_packet: delay=-185123 [ 75.982574] ccid3_hc_tx_send_packet: delay=-185167 [ 75.982716] ccid3_hc_tx_send_packet: delay=-185251 [ 75.982814] ccid3_hc_tx_send_packet: delay=-185290 [ 75.982996] cc ccid3_hc_tx_send_ ccid3_hc_tx_send_packet: delay=-243593 [ 76.097573] ccid3_hc_tx_send_packet: delay=-243658 [ 76.097689] ccid3_hc_tx_send_packet: delay=-243715 [ 76.097810] ccid3_hc_tx_send_packet: delay=-243778 [ 76.098044] ccid3_hc_tx_send_packet: delay=-243952 [ 76.098047] ccid3_hc_tx_update_win_count: now at 0X4 [ 76.098085] ccid3_hc_tx_send_packet: delay=-243934 [ 76.098167] ccid3_hc_tx_send_packet: delay=-243958 [ 76.098321] ccid3_hc_tx_send_packet: delay=-244053 [ 76.098426] ccid3_hc_tx_send_packet: delay=-244100 [ 76.098530] ccid3_hc_tx_send_packet: delay=-244145 [ 76.098649] ccid3_hc_tx_send_packet: delay=-244205 [ 76.098768] ccid3_hc_tx_send_packet: delay=-244265 [ 76.098914] ccid3_hc_tx_send_packet: delay=-244352 [ 76.099004] ccid3_hc_tx_send_packet: delay=-244384 [ 76.099122] ccid3_hc_tx_send_packet: delay=-244442 [ 76.099308] ccid3_hc_tx_send_packet: delay=-244570 [ 76.099367] ccid3_hc_tx_send_packet: delay=-244570 [ 76.099536] ccid3_hc_tx_send_packet: delay=-244680 [ 76.099539] ccid3_hc_tx_update_win_count: now at 0X5 [ 76.099607] ccid3_hc_tx_send_packet: delay=-244692 [ 76.099871] dccp_v4_rcv: ACK src9.133.209.65@5001 dst9.133.209.75@33438 seq4797824731, ack 51986876 [ 76.099880] ccid3_hc_tx_parse_options: client(f651c080), RECEIVE_RATE886477 [ 76.099884] ccid3_hc_tx_parse_options: client(f651c080), LOSS_EVENT_RATEB94967295 [ 76.099888] dccp_parse_options: client rx opt: TIMESTAMP8557, ackno 51986876 [ 76.099891] dccp_parse_options: client rx opt: NDP count1 [ 76.099896] ccid3_hc_tx_update_x: X_prev#754850, X_now#772954, X_calc=0, X_recv886477 [ 76.099900] ccid3_update_send_interval: t_ipiY, delta), s15, X#772954 [ 76.099905] ccid3_hc_tx_packet_recv: client(f651c080), RTTT54us (sampleU53us), s15, p=0, X_calc=0, X_recv886477, X#772954 [ 76.099932] ccid3_hc_tx_send_packet: delay=-244959 [ 76.099979] ccid3_hc_tx_send_packet: delay=-244947 [ 76.100020] ccid3_hc_tx_send_packet: delay=-244926 [ 76.100087] ccid3_hc_tx_send_packet: delay=-244937 [ 76.100244] ccid3_hc_tx_send_packet: delay=-245036 [ 76.100351] ccid3_hc_tx_send_packet: delay=-245083 [ 76.100445] ccid3_hc_tx_send_packet: delay=-245118 [ 76.100564] ccid3_hc_tx_send_packet: delay=-245179 [ 76.100767] ccid3_hc_tx_send_packet: delay=-245323 [ 76.100819] ccid3_hc_tx_send_packet: delay=-245316 [ 76.100954] ccid3_hc_tx_send_packet: delay=-245393 [ 76.100958] ccid3_hc_tx_update_win_count: now at 0X6 [ 76.101105] ccid3_hc_tx_send_packet: delay=-245484 [ 76.101163] ccid3_hc_tx_send_packet: delay=-245484 [ 76.101285] ccid3_hc_tx_send_packet: delay=-245547 [ 76.101478] ccid3_hc_tx_send_packet: delay=-245681 [ 76.101526] ccid3_hc_tx_send_packet: delay=-245670 [ 76.101701] ccid3_hc_tx_send_packet: delay=-245787 [ 76.101762] ccid3_hc_tx_send_packet: delay=-245788 [ 76.101882] ccid3_hc_tx_send_packet: delay=-245850 [ 76.102012] ccid3_hc_tx_send_packet: delay=-245921 [ 76.102121] ccid3_hc_tx_send_packet: delay=-245971 [ 76.102274] ccid3_hc_tx_send_packet: delay=-246065 [ 76.102424] ccid3_hc_tx_send_packet: delay=-246157 [ 76.102428] ccid3_hc_tx_update_win_count: now at 0X7 [ 76.102479] ccid3_hc_tx_send_packet: delay=-246153 [ 76.102608] ccid3_hc_tx_send_packet: delay=-246224 [ 76.102764] ccid3_hc_tx_send_packet: delay=-246320 [ 76.102960] ccid3_hc_tx_send_packet: delay=-246458 [ 76.103000] ccid3_hc_tx_send_packet: delay=-246438 [ 76.103174] ccid3_hc_tx_send_packet: delay=-246554 [ 76.103226] ccid3_hc_tx_send_packet: delay=-246548 [ 76.103313] ccid3_hc_tx_send_packet: delay=-246576 [ 76.103432] ccid3_hc_tx_send_packet: delay=-246636 [ 76.103552] ccid3_hc_tx_send_packet: del6346] ccid3_hc_tx_send_packet: delay=-298981 [ 76.206493] ccid3_hc_tx_send_packet: delay=-299069 [ 76.206497] ccid3_hc_tx_update_win_count: now at 0X0 [ 76.206585] ccid3_hc_tx_send_packet: delay=-299101 [ 76.206732] ccid3_hc_tx_send_packet: delay=-299190 [ 76.206823] ccid3_hc_tx_send_packet: delay=-299222 [ 76.207022] ccid3_hc_tx_send_packet: delay=-299363 [ 76.207061] ccid3_hc_tx_send_packet: delay=-299343 [ 76.207236] ccid3_hc_tx_send_packet: delay=-299459 [ 76.207352] ccid3_hc_tx_send_packet: delay=-299516 [ 76.207440] ccid3_hc_tx_send_packet: delay=-299546 [ 76.207577] ccid3_hc_tx_send_packet: delay=-299624 [ 76.207721] ccid3_hc_tx_send_packet: delay=-299709 [ 76.207798] ccid3_hc_tx_send_packet: delay=-299727 [ 76.207969] ccid3_hc_tx_send_packet: delay=-299839 [ 76.207972] ccid3_hc_tx_update_win_count: now at 0X1 [ 76.208055] ccid3_hc_tx_send_packet: delay=-299866 [ 76.208206] ccid3_hc_tx_send_packet: delay=-299959 [ 76.208280] ccid3_hc_tx_send_packet: delay=-299973 [ 76.208447] ccid3_hc_tx_send_packet: delay=-300082 [ 76.208521] ccid3_hc_tx_send_packet: delay=-300097 [ 76.208687] ccid3_hc_tx_send_packet: delay=-300204 [ 76.208752] dccp_v4_rcv: ACK src9.133.209.65@5001 dst9.133.209.75@33438 seq4797824751, ack 51987786 [ 76.208760] ccid3_hc_tx_parse_options: client(f651c080), RECEIVE_RATE883889 [ 76.208764] ccid3_hc_tx_parse_options: client(f651c080), LOSS_EVENT_RATEB94967295 [ 76.208768] dccp_parse_options: client rx opt: TIMESTAMP9465, ackno 51987786 [ 76.208771] dccp_parse_options: client rx opt: NDP count1 [ 76.208776] ccid3_hc_tx_update_x: X_prev#815306, X_now#767778, X_calc=0, X_recv883889 [ 76.208780] ccid3_update_send_interval: t_ipiY, delta), s15, X#767778 [ 76.208785] ccid3_hc_tx_packet_recv: client(f651c080), RTTT42us (sampleT55us), s15, p=0, X_calc=0, X_recv883889, X#767778 [ 76.208979] ccid3_hc_tx_send_packet: delay=-300438 [ 76.209022] ccid3_hc_tx_send_packet: delay=-300422 [ 76.209055] ccid3_hc_tx_send_packet: delay=-300396 [ 76.209243] ccid3_hc_tx_send_packet: delay=-300525
Hi there Gerrit,
I've been thinking a bit about this and can see what's happening here and with delays in general. There's a case here that I can't see the RFC covering and I'll send to the IETF list a follow up to this one.
It appears that in this case the sender can't keep up with the allowed transmit rate so the negative credit gets bigger and bigger. This is OK until we actually get some loss and then we won't be able to back off quickly.
The other scenario that this causes a problem if we don't reset t_nom is where we have idle periods. If we go idle for 10 seconds then we could potentially send heaps at that point to catch t_nom up. This doesn't seem right.
Ian
Quoted 10 lines · Gerrit Renker
Here is a log which I took after dropping the 3d patch which resets
t_nomwhen tnom <t_now. It shows that the negative credit does not clear, hence all packets are sent in one huge burst.[ 75.646215] ccid3_hc_tx_update_x: X_prev#743226, X_now#728510, X_calc=0, X_recv864255 [ 75.646218] ccid3_update_send_interval: t_ipiY, delta), s15, X#728510 [ 75.646223] ccid3_hc_tx_packet_recv: client(f651c080), RTTD98us (sampleU17us), s15, p=0, X_calc=0, X_recv864255, X#728510 [ 75.646264] ccid3_hc_tx_send_packet: delay=-14235 [ 75.646314] ccid3_hc_tx_send_packet: delay=-14226 [ 75.646451] ccid3_hc_tx_send_packet: delay=-14304
Signature · 3 lines
Web: http://wand.net.nz/~iam4 Blog: http://iansblog.jandi.co.nz WAND Network Research Group
Hi Ian,
thank you for this useful input. The cases are fully possible, with the test run (which had zero loss and no idle times) there would then be three cases where a larger backlog could occur.
I have been asking quite a few people about the scheduling granularity problem and got the following answers which may help deal with the third case (of the test run):
1) CCID 3 is probably restricted in its speed by the HZ parameter, i.e. trying to send more than HZ packets per second will likely lead to bursts. I found that the traffic shaping subsystem has similar problems, as the comments in the manpage of tc-tbf(8) indicate. So if we can make the system work predictably up to 15 Mbits/sec (HDTV bandwidth), I'd say that this would be pretty good (meaning to leave the rest for experimental / research extensions). It may have been not wise to expect very high bandwiths.
2) The following might cause problems:
* when the softirq for sending runs, it sends a whole bunch of packets
* each device has its own hardware queue
* additionally, each device has another Qdisc (FIFO) queue of usually 1000 packets
This may distort transmit packet spacings; a colleague further said that when the buffers / queues are mostly full (as at top speed), then the whole processing slows down (may be a hint for the too-high RTT estimates: in my test runs I get e.g. 5msec instead of 0.1msec)
3) We may get more predictable results with datagram-based bandwidth tests. I don't know the internals of iperf, but it seems that at the moment it tries to pipe as much data through the link as it is able to, so that during slow-start at some time X gets close to X_crit = packet_size_in_bytes * HZ. When using iperf as in `iperf -u', the bandwidth could be restricted, to be within the range controllable by CCID 3.
Gerrit
Quoting Ian McDonald:
| Hi there Gerrit, | | I've been thinking a bit about this and can see what's happening here | and with delays in general. There's a case here that I can't see the | RFC covering and I'll send to the IETF list a follow up to this one. | | It appears that in this case the sender can't keep up with the allowed | transmit rate so the negative credit gets bigger and bigger. This is | OK until we actually get some loss and then we won't be able to back | off quickly. | | The other scenario that this causes a problem if we don't reset t_nom | is where we have idle periods. If we go idle for 10 seconds then we | could potentially send heaps at that point to catch t_nom up. This | doesn't seem right. | | Ian | | On 16/01/07, Gerrit Renker <[email protected]> wrote: | > Here is a log which I took after dropping the 3d patch which resets t_nom when tnom < t_now. | > It shows that the negative credit does not clear, hence all packets are sent in one huge burst. | > | > | > [ 75.646215] ccid3_hc_tx_update_x: X_prev#743226, X_now#728510, X_calc=0, X_recv864255 | > [ 75.646218] ccid3_update_send_interval: t_ipiY, delta), s15, X#728510 | > [ 75.646223] ccid3_hc_tx_packet_recv: client(f651c080), RTTD98us (sampleU17us), s15, p=0, X_calc=0, X_recv864255, X#728510 | > [ 75.646264] ccid3_hc_tx_send_packet: delay=-14235 | > [ 75.646314] ccid3_hc_tx_send_packet: delay=-14226 | > [ 75.646451] ccid3_hc_tx_send_packet: delay=-14304 | |