Meaning of tcp_delack_min

Posted by Phi on Server Fault See other posts from Server Fault or by Phi
Published on 2010-12-11T18:04:02Z Indexed on 2010/12/22 1:56 UTC
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linux

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tcp

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linux-kernel

Hi,

the current Linux Kernel (e.g. 2.6.36) uses Delayed Acknowledgments (delack).

In /include/net/tcp.h it says:

define TCP_DELACK_MIN ((unsigned)(HZ/25))

So, for a Kernel using a HZ value of 1000, an ACK should be delayed by a minimum of 40 ms.

However, RFC 2581 says a TCP implementation should acknowledge every second full sized segment without further delay.

Does anybody know whether the Linux Kernel follows that 'should' or whether the TCP_DELACK_MIN value means that even after a full sized segment was received, the ACK continues to be delayed until 40 ms have passed?

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