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

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Date:	Wed, 22 Aug 2007 12:33:04 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	David Miller <davem@...emloft.net>
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

Hi Dave,

David Miller <davem@...emloft.net> wrote on 08/22/2007 09:52:29 AM:

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

Does turning off batching solve that problem? What I mean by that is:
batching can be disabled if a TSO device is worse for some cases. Infact
something that I had changed my latest code is to not enable batching
in register_netdevice (in Rev4 which I am sending in a few mins), rather
the user has to explicitly turn 'on' batching.

Wondering if that is what you are concerned about. In any case, I will
test your case on Monday (I am on vacation for next couple of days).

Thanks,

- KK

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