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Date
SubjectRe: slow tcp acks on loopback device
From
From: Steve French <smfltc@us.ibm.com>
Date: 22 Jul 2005 14:56:59 -0500

> Noticing that the loopback device (at least on RHEL4) has an unfortunate
> mtu size 16384 (which is about 50 bytes too small for SMB read
> responses), I did try increasing the MTU slightly. Changing that to
> 18000 did avoid the fragmentation and the 40ms delay - but what puzzled
> me was why setting TCP_NODELAY after the socket was created did not
> eliminate the delay on the ack and if there is a way to avoid the huge
> tcp ack delay by either doing something else to force client acking
> immediately or to do something on the client side of the stack to get
> the server to send the whole 16K+ frame - it looks like the tcp windows
> is 32K if the value in the tcp acks in the network trace is to be
> trusted.

TCP_NODELAY does not control ACK generation, instead it modifies
the Nagle algorithm behavior when sending data packets.

Please take networking discussions to netdev@vger.kernel.org which
is where the networking developers are.
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