netdev - Re: [PATCH net-next] net/mlx4_en: remove NETDEV_TX

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Message-Id: <20141007.132102.2147742408943394634.davem@davemloft.net>
Date:	Tue, 07 Oct 2014 13:21:02 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	amirv@...lanox.com, amirv.mellanox@...il.com
Cc:	eric.dumazet@...il.com, edumazet@...gle.com,
	netdev@...r.kernel.org, yevgenyp@...lanox.com,
	ogerlitz@...lanox.com, idos@...lanox.com
Subject: Re: [PATCH net-next] net/mlx4_en: remove NETDEV_TX_BUSY

From: Amir Vadai <amirv.mellanox@...il.com>
Date: Tue, 07 Oct 2014 11:30:06 +0300

> On 10/6/2014 7:30 PM, Eric Dumazet wrote:
>> From: Eric Dumazet <edumazet@...gle.com>
>> 
>> Drivers should avoid NETDEV_TX_BUSY as much as possible.
>> 
>> They should stop the tx queue before qdisc even tries to push another
>> packet, to avoid requeues.
>> 
>> For a driver supporting skb->xmit_more, this is likely to be a prereq
>> anyway, otherwise we could have a tx deadlock : We need to force a
>> doorbell if TX ring is full.
>> 
>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>> ---
> 
> Reviewed. Also verified that it fixes the deadlock (by sending a large
> burst - larger than ring size). Before this fix, last packet of the
> burst wasn't sent, therefore no doorbell was rang, and the queue was
> stalled.
> 
> BTW, another nice optimization that we hope to send soon, is not to arm
> the CQ unless ringing the doorbell.
> 
> Acked-by: Amir Vadai <amirv@...lanox.com>

Applied, thanks everyone.
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