Re: bin/60443: ftp ASCII transfers are too slow

The following reply was made to PR bin/60443; it has been noted by GNATS.

From: [email protected] (Michael van Elst)
To: [email protected]
Cc: 
Subject: Re: bin/60443: ftp ASCII transfers are too slow
Date: Mon, 13 Jul 2026 05:32:32 -0000 (UTC)

 [email protected] ("RVP via gnats") writes:
 
 > I don't know how you're getting 35MB/sec w/o any tweaking. Michael, can you try
 > with both server and client on localhost like I did?
 
 
 localhost gets:
 
 ftp> get in.txt
 local: in.txt remote: in.txt
 229 Entering Extended Passive Mode (|||61368|)
 150 Opening ASCII mode data connection for 'in.txt' (306788817 bytes).
 226 Transfer complete.
 312122680 bytes received in 00:12 (23.66 MiB/s)
 
 
 > 04:43:22.966644 IP6 ::1.65425 > ::1.65424: Flags [P.], seq 314369:328705, ack 1, win 4096, options [nop,nop,TS val 7 ecr 7], length 14336
 
 + 200ms
 
 > 04:43:23.166607 IP6 ::1.65424 > ::1.65425: Flags [.], ack 328705, win 4096, options [nop,nop,TS val 7 ecr 7], length 0
 
 + 0ms
 
 > 04:43:23.166636 IP6 ::1.65425 > ::1.65424: Flags [P.], seq 328705:342017, ack 1, win 4096, options [nop,nop,TS val 7 ecr 7], length 13312
 
 + 200ms
 
 > 04:43:23.366620 IP6 ::1.65424 > ::1.65425: Flags [.], ack 342017, win 4096, options [nop,nop,TS val 7 ecr 7], length 0
 
 
 Looks more like the ACKs are delayed and less like Nagle's algorithm. No
 idea what is happening.
 
 
 Here it looks like:
 
 
 
 06:42:26.105109 IP6 ::1.55463 > ::1.55464: Flags [SEW], seq 919247764, win 65535, options [mss 33116,nop,wscale 8,sackOK,TS val 1 ecr 0], length 0
 06:42:26.105243 IP6 ::1.55464 > ::1.55463: Flags [S.E], seq 929186746, ack 919247765, win 65535, options [mss 33116,nop,wscale 8,sackOK,TS val 1 ecr 1], length 0
 06:42:26.105357 IP6 ::1.55463 > ::1.55464: Flags [.], ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.106828 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 1:1025, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 1024
 06:42:26.108062 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 1025:17409, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 16384
 06:42:26.108202 IP6 ::1.55463 > ::1.55464: Flags [.], ack 17409, win 190, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.108391 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 17409:18433, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 1024
 06:42:26.109663 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 18433:34817, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 16384
 06:42:26.109774 IP6 ::1.55463 > ::1.55464: Flags [.], ack 34817, win 122, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.109953 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 34817:35841, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 1024
 06:42:26.111083 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 35841:52225, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 16384
 06:42:26.111189 IP6 ::1.55463 > ::1.55464: Flags [.], ack 52225, win 54, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.111367 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 52225:53249, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 1024
 06:42:26.158231 IP6 ::1.55463 > ::1.55464: Flags [.], ack 53249, win 50, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.274512 IP6 ::1.55463 > ::1.55464: Flags [.], ack 53249, win 182, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.274573 IP6 ::1.55464 > ::1.55463: Flags [.], seq 53249:69633, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 16384
 06:42:26.274624 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 69633:83969, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 14336
 06:42:26.274669 IP6 ::1.55463 > ::1.55464: Flags [.], ack 83969, win 62, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.274734 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 83969:84993, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 1024
 06:42:26.275839 IP6 ::1.55463 > ::1.55464: Flags [.], ack 84993, win 190, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.275905 IP6 ::1.55464 > ::1.55463: Flags [.], seq 84993:109569, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 24576
 06:42:26.275949 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 109569:129025, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 19456
 06:42:26.275988 IP6 ::1.55463 > ::1.55464: Flags [.], ack 129025, win 18, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.276154 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 129025:130049, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 1024
 06:42:26.277550 IP6 ::1.55463 > ::1.55464: Flags [.], ack 130049, win 146, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.277616 IP6 ::1.55464 > ::1.55463: Flags [.], seq 130049:163153, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.278857 IP6 ::1.55463 > ::1.55464: Flags [.], ack 163153, win 149, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.278976 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 163153:195585, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 32432
 06:42:26.280471 IP6 ::1.55463 > ::1.55464: Flags [.], ack 195585, win 154, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.280526 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 195585:211969, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 16384
 06:42:26.281981 IP6 ::1.55463 > ::1.55464: Flags [.], ack 211969, win 222, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.282060 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 211969:218113, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 6144
 06:42:26.282665 IP6 ::1.55464 > ::1.55463: Flags [.], seq 218113:251217, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.282715 IP6 ::1.55463 > ::1.55464: Flags [.], ack 251217, win 125, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.282753 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 251217:251905, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 688
 06:42:26.283889 IP6 ::1.55463 > ::1.55464: Flags [.], ack 251905, win 254, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.283963 IP6 ::1.55464 > ::1.55463: Flags [.], seq 251905:285009, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.284018 IP6 ::1.55464 > ::1.55463: Flags [P.], seq 285009:316417, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 31408
 06:42:26.284067 IP6 ::1.55463 > ::1.55464: Flags [.], ack 316417, win 2, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.285539 IP6 ::1.55463 > ::1.55464: Flags [.], ack 316417, win 134, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.285610 IP6 ::1.55464 > ::1.55463: Flags [.], seq 316417:349521, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.286814 IP6 ::1.55463 > ::1.55464: Flags [.], ack 349521, win 137, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.286884 IP6 ::1.55464 > ::1.55463: Flags [.], seq 349521:382625, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.288301 IP6 ::1.55463 > ::1.55464: Flags [.], ack 382625, win 140, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.288398 IP6 ::1.55464 > ::1.55463: Flags [.], seq 382625:415729, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.289602 IP6 ::1.55463 > ::1.55464: Flags [.], ack 415729, win 142, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.289676 IP6 ::1.55464 > ::1.55463: Flags [.], seq 415729:448833, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.291107 IP6 ::1.55463 > ::1.55464: Flags [.], ack 448833, win 145, options [nop,nop,TS val 1 ecr 1], length 0
 06:42:26.291176 IP6 ::1.55464 > ::1.55463: Flags [.], seq 448833:481937, ack 1, win 258, options [nop,nop,TS val 1 ecr 1], length 33104
 06:42:26.292396 IP6 ::1.55463 > ::1.55464: Flags [.], ack 481937, win 148, options [nop,nop,TS val 1 ecr 1], length 0
 
 ...
 
 06:42:28.345968 IP6 ::1.55464 > ::1.55463: Flags [.], seq 49301969:49335073, ack 1, win 258, options [nop,nop,TS val 5 ecr 5], length 33104
 06:42:28.346052 IP6 ::1.55464 > ::1.55463: Flags [.], seq 49335073:49368177, ack 1, win 258, options [nop,nop,TS val 5 ecr 5], length 33104
 06:42:28.346108 IP6 ::1.55463 > ::1.55464: Flags [.], ack 49368177, win 41, options [nop,nop,TS val 5 ecr 5], length 0
 06:42:28.348542 IP6 ::1.55463 > ::1.55464: Flags [.], ack 49368177, win 301, options [nop,nop,TS val 5 ecr 5], length 0
 06:42:28.348625 IP6 ::1.55464 > ::1.55463: Flags [.], seq 49368177:49401281, ack 1, win 258, options [nop,nop,TS val 5 ecr 5], length 33104
 06:42:28.348701 IP6 ::1.55464 > ::1.55463: Flags [.], seq 49401281:49434385, ack 1, win 258, options [nop,nop,TS val 5 ecr 5], length 33104
 06:42:28.348752 IP6 ::1.55463 > ::1.55464: Flags [.], ack 49434385, win 43, options [nop,nop,TS val 5 ecr 5], length 0
 06:42:28.351214 IP6 ::1.55463 > ::1.55464: Flags [.], ack 49434385, win 303, options [nop,nop,TS val 5 ecr 5], length 0