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

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Message-ID: <20080201092439.7c588ef5@extreme>
Date:	Fri, 1 Feb 2008 09:24:39 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	Patrick McHardy <kaber@...sh.net>,
	Andi Kleen <andi@...stfloor.org>, Glen Turner <gdt@....id.au>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] Disable TSO for non standard qdiscs

On Fri, 1 Feb 2008 15:34:21 +0100
Andi Kleen <andi@...stfloor.org> wrote:

> > 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

I wish there was a per-device setting for the max-size of TSO burst.


-- 
Stephen Hemminger <stephen.hemminger@...tta.com>
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