netdev - Re: [PATCH 2/2] qdisc_restart - couple of optimizations.

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Date:	Thu, 14 Jun 2007 21:21:11 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
Cc:	kumarkr@...ux.vnet.ibm.com, davem@...emloft.net, jamal@...erus.ca,
	tgraf@...g.ch, kaber@...sh.net, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] qdisc_restart - couple of optimizations.

On Wed, Jun 13, 2007 at 10:51:00AM -0700, Waskiewicz Jr, Peter P wrote:
> 
> I somewhat disagree here.  The underlying driver can conceivably stop
> the device queue even if the stack holds the queue lock during an
> interrupt to clean Tx descriptors, and it finds it's out of them or
> needs to grab the device for whatever reason.  Granted this is a corner
> case, and the net effect would be a simple requeue of the skb, but
> checking the status of the queue at the last possible moment before
> entering the driver could alleviate the requeue in the time between
> ->dequeue() from the qdisc, and hard_start_xmit() if an event like I
> mentioned happened.

IMHO this scenario occurs so infrequently that the check isn't worth it
especially since the driver has to be able to deal with us calling it
after netif_stop_queue() anyway.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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