netdev - Re: [ofa-general] Re: [PATCH 2/3][NET

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Date:	Thu, 11 Oct 2007 12:22:23 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	andi@...stfloor.org, 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, mcarlson@...adcom.com,
	mchan@...adcom.com, netdev@...r.kernel.org,
	peter.p.waskiewicz.jr@...el.com, randy.dunlap@...cle.com,
	rdreier@...co.com, Robert.Olsson@...a.slu.se,
	shemminger@...ux-foundation.org, sri@...ibm.com, tgraf@...g.ch
Subject: Re: [ofa-general] Re: [PATCH 2/3][NET_BATCH] net core use batching

Hi Dave,

David Miller wrote on 10/10/2007 02:13:31 AM:

> > Hopefully that new qdisc will just use the TX rings of the hardware
> > directly. They are typically large enough these days. That might avoid
> > some locking in this critical path.
>
> Indeed, I also realized last night that for the default qdiscs
> we do a lot of stupid useless work.  If the queue is a FIFO
> and the device can take packets, we should send it directly
> and not stick it into the qdisc at all.

Since you are talking of how it should be done in the *current* code,
I feel LLTX drivers will not work nicely with this.

Actually I was trying this change a couple of weeks back, but felt
that doin go would result in out of order packets (skbs present in
q which were not sent out for LLTX failure will be sent out only at
next net_tx_action, while other skbs are sent ahead).

One option is to first call qdisc_run() and then process this skb,
but that is ugly (requeue handling).

However I guess this can be done cleanly once LLTX is removed.

Thanks,

- KK

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