Date: Thu, 10 May 2012 14:46:58 -0500
From: Jonathan Nieder <jrnieder@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: alexander.h.duyck@intel.com, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        torvalds@linux-foundation.org, akpm@linux-foundation.org,
        alan@lxorguk.ukuu.org.uk, stephen.s.ko@intel.com,
        jeffrey.t.kirsher@intel.com
Subject: Re: [ 33/52] net: Fix issue with netdev_tx_reset_queue not resetting
 queue from XOFF state
Message-ID: <20120510194658.GA9858@burratino>
References: <20120510173135.772550373@linuxfoundation.org>
 <4FAC0EA7.3000100@intel.com>
 <20120510.145510.1040533529305157641.davem@davemloft.net>
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David Miller wrote:
> From: Alexander Duyck <alexander.h.duyck@intel.com>

>> All of the changes in igb are unnecessary.  I think they can be dropped
>> from the patch as they have already been reverted from the latest
>> net-next.  The only change that is really needed is the piece in
>> netdevice.h below.
>
> Does it hurt?  If not, just let it be.

Based on the commit description for dad8a3b3eaa0 ("igb, ixgbe:
netdev_tx_reset_queue incorrectly called from tx init path"), yes, it
hurts.  I don't know if it hurts enough to justify holding up this
patch until dad8a3b3eaa0 hits mainline.

|                            this sort of works in most cases except
| when the number of real tx queues changes. When the number of real
| tx queues changes netdev_tx_reset_queue() only gets called on the
| new number of queues so when we reduce the number of queues we risk
| triggering the watchdog timer and repeated device resets.
|
| So this is not only a cosmetic issue but causes real bugs. For
| example enabling/disabling DCB or FCoE in ixgbe will trigger this.
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