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

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Message-ID: <20071012100500.02255243@freepuppy.rosehill>
Date:	Fri, 12 Oct 2007 10:05:00 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
Cc:	"Andi Kleen" <andi@...stfloor.org>,
	"David Miller" <davem@...emloft.net>, <hadi@...erus.ca>,
	<jeff@...zik.org>, <johnpol@....mipt.ru>,
	<herbert@...dor.apana.org.au>, <gaagaan@...il.com>,
	<Robert.Olsson@...a.slu.se>, <netdev@...r.kernel.org>,
	<rdreier@...co.com>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	<mcarlson@...adcom.com>, <jagana@...ibm.com>,
	<general@...ts.openfabrics.org>, <mchan@...adcom.com>,
	<tgraf@...g.ch>, <randy.dunlap@...cle.com>, <sri@...ibm.com>,
	<kaber@...sh.net>
Subject: Re: [ofa-general] Re: [PATCH 2/3][NET_BATCH] net core use batching

On Fri, 12 Oct 2007 09:08:58 -0700
"Brandeburg, Jesse" <jesse.brandeburg@...el.com> wrote:

> Andi Kleen wrote:
> >> When the hw TX queue gains space, the driver self-batches packets
> >> from the sw queue to the hw queue.
> > 
> > I don't really see the advantage over the qdisc in that scheme.
> > It's certainly not simpler and probably more code and would likely
> > also not require less locks (e.g. a currently lockless driver
> > would need a new lock for its sw queue). Also it is unclear to me
> > it would be really any faster.
> 
> related to this comment, does Linux have a lockless (using atomics)
> singly linked list element?  That would be very useful in a driver hot
> path.

Use RCU? or write a generic version and get it reviewed.  You really
want someone with knowledge of all the possible barrier impacts to
review it.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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