netdev - Re: [PATCH] Disable TSO for non standard qdiscs

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Message-ID: <20080201143421.GB16630@one.firstfloor.org>
Date:	Fri, 1 Feb 2008 15:34:21 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	Andi Kleen <andi@...stfloor.org>, Glen Turner <gdt@....id.au>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] Disable TSO for non standard qdiscs

> The TSO defer logic is based on your congestion window and current
> window size.  So the actual frame sizes hitting your NIC attached to
> your DSL probably aren't anywhere near 64KB, but probably more in line
> with whatever your window size is for DSL.

DSL windows can be quite large because a lot of DSL lines have a quite
long latency due to error correction. And with ADSL2 we have upto 16Mbit
now.

> I think we're having more of a disagreement of what is considered the
> "normal case" user.  If you are on a slow link, such as a DSL/cable
> line, your TCP window/congestion window aren't going to be big enough to
> generate large TSO's, so what is the issue?  But disabling TSO, say on a

64k TSOs are likely even with DSL. Anyways even with smaller TSOs the
change still makes sense because each increase makes packet scheduling
less smooth.

-Andi
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