[ofa-general] net.ipv4.tcp_timestamps

[John Russo]

Does anyone know why this value is being altered by OFED?
 
"net.ipv4.tcp_timestamps" is being set to 0 during OFED installation.  
 
Default value of this parameter is set to 1 on standard RHEL/SLES
distros which OFED installation script modifies to 0.  Also, when OFED
is uninstalled, it does not reset these sysctl parameters to their
original values.
 
This parameter is specifically recommended to be turned ON for High
performance network.  This is a TCP option that can be used to calculate
the Round Trip Measurement in a better and more accurate way than the
retransmission timeout method can.  Accurate value of retransmission
timeout should be determined to avoid unnecessary retransmissions and
hence to improve TCP performance.  RFC 1323 talks about this TCP
extension for High Performance.  
 
When the parameter net.ipv4.tcp_timestamps=1, then it adds extra 12
bytes into TCP header increasing its size.  This has an obvious effect
of decrease in bandwidth as we have some extra data flowing.  Is this
the reason why OFED turns it OFF to net.ipv4.tcp_timestamps=0.
 

 

 

 
__________________________
John F. Russo
Manager, Engineering
QLogic Corporation
780 Fifth Avenue, Suite 140
King of Prussia, PA 19406
Direct: 610-233-4866
Main: 610-233-4800
Fax: 610-233-4777
Cell: 610-246-9903
Email: John.Russo at qlogic.com <mailto:John.Russo at qlogic.com> 
www.qlogic.com <http://www.qlogic.com> 

 

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