netdev - Re: [PATCH 0/9 Rev3] Implement batching skb API and support in IPoIB

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Date:	Tue, 21 Aug 2007 21:22:29 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	krkumar2@...ibm.com
Cc:	gaagaan@...il.com, general@...ts.openfabrics.org, hadi@...erus.ca,
	herbert@...dor.apana.org.au, jagana@...ibm.com, jeff@...zik.org,
	johnpol@....mipt.ru, kaber@...sh.net, kumarkr@...ux.ibm.com,
	mcarlson@...adcom.com, mchan@...adcom.com, netdev@...r.kernel.org,
	peter.p.waskiewicz.jr@...el.com, rdreier@...co.com,
	rick.jones2@...com, Robert.Olsson@...a.slu.se,
	shemminger@...ux-foundation.org, sri@...ibm.com, tgraf@...g.ch,
	xma@...ibm.com
Subject: Re: [PATCH 0/9 Rev3] Implement batching skb API and support in
 IPoIB

From: Krishna Kumar2 <krkumar2@...ibm.com>
Date: Wed, 22 Aug 2007 09:41:52 +0530

> David Miller <davem@...emloft.net> wrote on 08/22/2007 12:21:43 AM:
> 
> > From: jamal <hadi@...erus.ca>
> > Date: Tue, 21 Aug 2007 08:30:22 -0400
> >
> > > On Tue, 2007-21-08 at 00:18 -0700, David Miller wrote:
> > >
> > > > Using 16K buffer size really isn't going to keep the pipe full enough
> > > > for TSO.
> > >
> > > Why the comparison with TSO (or GSO for that matter)?
> >
> > Because TSO does batching already, so it's a very good
> > "tit for tat" comparison of the new batching scheme
> > vs. an existing one.
> 
> I am planning to do more testing on your suggestion over the
> weekend, but I had a comment. Are you saying that TSO and
> batching should be mutually exclusive so hardware that doesn't
> support TSO (like IB) only would benefit?
> 
> But even if they can co-exist, aren't cases like sending
> multiple small skbs better handled with batching?

I'm not making any suggestions, so don't read that into anything I've
said :-)

I think the jury is still out, but seeing TSO perform even slightly
worse with the batching changes in place would be very worrysome.
This applies to both throughput and cpu utilization.
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