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Re: inetutils 1.5 / ftpd problem: 426 Data connection: No buffer space available.

antony baxter wrote:

Unfortunately, with XP SP2, Cygwin 1.5 as the server machine, I get
pretty much the same symptoms with each of the above ftpds serving up
a 350mb file:

1. In all cases, the ftpd process' memory usage increases to ~350mb,
2. As the buffer value decreases, the process' cpu usage increases
(ftpd-1k.exe used about 75% of the cpu vs. about 10% for ftpd-8k.exe),
3. Performance jumped around (ftpd-1k transferred the file in
90seconds, ftpd-4k in 166 seconds, ftp-8k in 114 seconds on a wired

Quick addendum: I copied over in.ftpd.exe from another Cygwin installation running inetutils 1.3.2 and symlinked it to ftpd on my server; using that to serve the same file, memory usage sticks at 3500kb, cpu usage never rises about 5%, and the file was delivered in 194 seconds.

Well, one of the differences between ftpd-1.3.2 and ftpd-1.5 is that the newer version uses mmap on the (local) file. ftpd.c is the /only/ source file in inetutils that uses mmap.

So, I recompiled with HAVE_MMAP turned off (but still using 4k chunks). Give this a try:

I get behavior here which is very similar to what I reported for the 4k-WITH-mmap version:
(1) sane memory profile
(2) topology one, 9-10 Mbps 2-3% cpu
(3) topology two, 14-15 Mbps, 4-6% cpu [*]

I'm not sure what benefit mmap has in this case -- unless you can exploit some zero-copy kernel code for transferring data from disk to ethernet device. But I don't think Windows has anything like that. I certainly don't *see* any benefit, in my limited testing on this set of hardware.

If this *does* fix the problem, it may point to an issue with cygwin-1.5's mmap implementation, or with XP's handling of the underlying NtCreateSection()...mmap is not supposed to be CPU-intensive.


[*] However, with the mmap'ed, 4k buffer version, I also saw only 4-6% CPU utilization on Vista, cygwin-1.7. So, YMMV.

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