Messages in this thread | | | Date | Fri, 17 Sep 1999 23:26:15 +0200 | From | Karsten Keil <> | Subject | network problem |
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Hello anybody,
I try to make some research on the network slowdown problem, which was reported from some people. In some case the shutoff of tcp_timestamps was helping, but in other cases not. I don't saw this problem on my machine up to now, but during some test I saw other strange things. I the moment I run 2.2.13pre7 (+ ISDN from 2.2.13pre8) but the same was under plain 2.2.12. Here a short description of my "test bench":
I make uploads with scp (a ~400K .gz file) over a 64k rawip ISDN line rate is about 6.6K/s (not optimum, but reliable). The strange things are the observation on begin and end of the transmit, which I don't understand.
the statistics from scp shows following:
1-2 sec after start 140-160K are transfered after ~35 sec the transfer is 100% after ~60 sec the transfer is finished (I got the prompt back).
a netstat -c -t shows allways 40k-60K in Send-Q
the 40k-60K in Send-Q came from a (too big I know) dev->tx_queue_len value in the ISDN network devive, but where are the other 100K ?
If I try to change tx_queue_len with ifconfig, it don't change anything, only the new value is displayed in ifconfig. If I change it in source code the new value is used and here are only 3-6K in Send-Q (with tx_queue_len =5), but here also 140K in buffers after few seconds. /proc/sys/net/core/wmem_max is 64K, if I change this with echo -n "8192"... same behaviour.
This is no problem for me, because the allover rate is OK here, but I like to understand where and why so much data is buffered somewhere, because I believe that this may have something to do with the other problem (network slowdown). With this problem one people saw following: Networking over an sync ppp ISDN line slows down, a ping freezed. He started tcpdump on the interface and saw that no packets are going out. netstat shows data in Send-Q. The ISDN is open and idle. He was starting a second ping and now pakets are going out, but also from the old ping every second, so I suspect somewhere a queue or buffer is blocked. Unfortunatly this case isn't stable, it occours in the moment ones a week and so he can't make more tests.
Karsten Keil
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