Date: Mon, 6 Oct 2003 15:33:15 -0400 (EDT) From: Carl Mascott <cmascott@att.net> To: freebsd-net@freebsd.org Subject: 4.8-R: problem when tcp.recvspace=56K (default) Message-ID: <200310061933.h96JXFY8000505@callisto.local>
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FreeBSD 4.8-R kernel.GENERIC
user ppp
P II - 400
128 MB RAM
56K ext. modem, 45.3K connection
Something in the socket/proto/network interface area doesn't
work correctly when tcp.recvspace=56K, the default value in 4.8-R.
It DOES work correctly when tcp.recvspace= 16K, 32K, 48K.
I see the following repeatable problem. At the same point in
the ftp reception of a 218K .gz file, received data stops getting
delivered to the ftp client and starts stacking up in mbufs.
The ftp client reports "stalled". When the recvspace limit
is reached, the entire socket receive buffer is delivered to
the ftp client as fast as the client can take it. For the
remainder of the file transfer there are no further ftp
client stalls. Note that the stall occurs at approx.
2 * tcp.recvspace.
Please note that this stall would not be perceptible on a
LAN: the 56K socket receive buffer would fill up too quickly.
This would be mostly harmless were it not for the extra mbufs
being consumed. On a system with many TCP connections the
supply of mbufs might be exhausted.
Following is a log of my activities in trying to track
down this problem. I haven't been able to pinpoint it.
Does anyone have any idea what it might be or how to
further track it down?
10/05/03
Start: tcp.recvspace=48K
ftp receive 218K .gz file
no ftp client stalls
netstat -m
191/224/6016 mbufs in use (current/peak/max):
189 mbufs allocated to data
2 mbufs allocated to packet headers
130/146/1504 mbuf clusters in use (current/peak/max)
348 Kbytes allocated to network (7% of mb_map in use)
0 requests for memory denied
0 requests for memory delayed
0 calls to protocol drain routines
Change tcp.recvspace=56K (default)
ftp receive 218K .gz file
ftp client stalls @ 113K for ~10 seconds, then jumps to 170K
ftp client reports "stalled"
no modem RxD stall
netstat -w 2 -I tun0 shows no stall in tun0 input.
netstat -m
192/464/6016 mbufs in use (current/peak/max):
190 mbufs allocated to data
2 mbufs allocated to packet headers
130/146/1504 mbuf clusters in use (current/peak/max)
408 Kbytes allocated to network (9% of mb_map in use)
0 requests for memory denied
0 requests for memory delayed
0 calls to protocol drain routines
Consumed 464-224=240 extra mbufs, no extra mbuf clusters
408-348=60 KB additional RAM allocated to network
Note: MSIZE=256 (machine/param.h)
Note: No stall w/ tcp.recvspace = 16K, 32K, 48K.
Tried ftp -d: echoed all commands sent to host, but
didn't appear to produce any socket/proto debug output.
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