netdev - Re: [PATCH 0/2] Get rid of ndo_xmit

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Message-Id: <20140901.145646.174847768842584425.davem@davemloft.net>
Date:	Mon, 01 Sep 2014 14:56:46 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	netdev@...r.kernel.org, therbert@...gle.com, jhs@...atatu.com,
	edumazet@...gle.com, jeffrey.t.kirsher@...el.com,
	rusty@...tcorp.com.au, dborkman@...hat.com, brouer@...hat.com,
	john.r.fastabend@...el.com
Subject: Re: [PATCH 0/2] Get rid of ndo_xmit_flush

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Mon, 01 Sep 2014 22:05:42 +0200

> But as soon as we try to make Qdiscs absolutely lockless, we don't have
> any guard that we don't concurrently dequeue skbs from it and suddenly
> one Qdisc dequeue processing entity couldn't notify the driver that the
> end of the batching was reached. I think this could become a problem
> depending on how much of the locking is removed?

I am certain that batching will require taking the device transmit
lock over the ->ndo_start_xmit() invocations, and therefore the
deferral decisions must atomically be made inside of that context.
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