Slow tcp handshakes rate of 2.6.20 and 2.6.19

From: Quan Sun
Date: Thu Apr 26 2007 - 22:36:44 EST


Hi,
In these days I met a strange situation, tcp handshake rate is
slow after 2.6.18.8.

The case is, server accepts connections, and records number of successful
tcp handshakes during last 10 seconds. Client tries to connect to server's
listen port as fast as possible and as many as possible, or in simple words,
client use connect() to flood the server. In both cases, there are a log of syn
re-send.

Server's performances varied much, depending on which kernel it was
running. On 2.6.18.8, 10000 successful connections take about 30-40 seconds,
while on 2.6.20 or 2.6.19, it will cost about more than 5 minutes.

It seems there is some a mechanism which prevents connect() flood.
My problem is, is the mechanism exist, or there is some other reason(s)
for why 2.6.18 varies from 2.6.19/2.6.20?

All these config files are all the same, tcp related options are,
CONFIG_INET_TCP_DIAG=m
CONFIG_TCP_CONG_ADVANCED=y
CONFIG_TCP_CONG_BIC=y
CONFIG_TCP_CONG_CUBIC=m
CONFIG_TCP_CONG_WESTWOOD=m
CONFIG_TCP_CONG_HTCP=m
CONFIG_TCP_CONG_HSTCP=m
CONFIG_TCP_CONG_HYBLA=m
CONFIG_TCP_CONG_VEGAS=m
CONFIG_TCP_CONG_SCALABLE=m
CONFIG_TCP_CONG_LP=m
CONFIG_TCP_CONG_VENO=m
CONFIG_IP_VS_PROTO_TCP=y
CONFIG_NETFILTER_XT_MATCH_TCPMSS=m
CONFIG_IP_NF_TARGET_TCPMSS=m


--
Quan Sun
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