Re: Very poor TCP/SACK performance

David S. Miller (davem@dm.cobaltmicro.com)
Tue, 8 Sep 1998 05:18:38 -0700


From: alan@lxorguk.ukuu.org.uk (Alan Cox)
Date: Tue, 8 Sep 1998 14:13:48 +0100 (BST)

> The problem is, with the default settings we are pretty safe
> about buffer overcommit. It also makes "I'm going to send you
> out of order

In 2.0.x I used 100% overcommit. With ethernet drivers doing
rx_copybreak that comes out about right in the wash. It was
originally a finger in air and gues exercise but it turned out near
enough right

Ok, right.

The issue is to get the max benefit of SACK with even moderately
latent paths we need to up it a bit, this is the crux of all the
complaints we are getting.

So my question is, can we up the default safely and if so by how much?

One thing you could do is compute the "average RAM in machine"
quantum at the time you made your settings for 2.0.x, and do the same
for now, and compute the interest compounded continuously. :-)

Later,
David S. Miller
davem@dm.cobaltmicro.com

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