netdev - Re: tcp bw in 2.6

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Message-ID: <4702A19E.5090403@hp.com>
Date:	Tue, 02 Oct 2007 12:53:02 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Larry McVoy <lm@...mover.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, davem@...emloft.net,
	wscott@...mover.com, netdev@...r.kernel.org
Subject: Re: tcp bw in 2.6

> I also would have expected more ACK's from the HP box. It's been a long 
> time since I did TCP, but I thought the rule was still that you were 
> supposed to ACK at least every other full frame - but the HP box is acking 
> roughly every 16K (and it's *not* always at TSO boundaries: the earlier 
> ACK's in the sequence are at 1460-byte packet boundaries, but it does seem 
> to end up getting into that pattern later on).

Drift...

The RFC's say "SHOULD" (emphasis theirs) rather than "MUST."

Both HP-UX and Solaris have rather robust ACK avoidance heuristics to cut-down 
on the CPU overhead of bulk transfers.  (That they both have them stems from 
their being cousins, sharing a common TCP stack ancestor long ago - both of 
course have been diverging since then).

rick jones
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