netdev - Re: [net-next 04/14] net: Fix issue with netdev_tx_reset_queue not resetting queue from XOFF state

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Date:	Sat, 21 Apr 2012 16:18:42 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	john.r.fastabend@...el.com
Cc:	therbert@...gle.com, alexander.duyck@...il.com,
	alexander.h.duyck@...el.com, jeffrey.t.kirsher@...el.com,
	netdev@...r.kernel.org, gospo@...hat.com, sassmann@...hat.com
Subject: Re: [net-next 04/14] net: Fix issue with netdev_tx_reset_queue not
 resetting queue from XOFF state

From: John Fastabend <john.r.fastabend@...el.com>
Date: Sat, 21 Apr 2012 09:27:31 -0700

> On 4/20/2012 11:01 PM, Tom Herbert wrote:
>>> I don't recall the exact reason now, as John said I think it had to do
>>> with the ethtool tests not using the same cleanup routine and leaving
>>> us in a bad state.  I am pretty sure there was some path in which
>>> where the call was didn't work but I do not recall the exact details
>>> now.  Most of the reason for moving it is due to the fact that the
>>> reset is now also clearing the bit, and from the driver perspective we
>>> didn't need it in two places.  After looking it all over again, I
>>> suppose this causes a cosmetic issue for the bql "inflight" statistic
>>> in sysfs since the value will be retained until the interface is
>>> brought back up with this change.  Is that an issue or something that
>>> can be lived with since the interface isn't active anyway in this
>>> case?
>>>
>> On the surface, it seems cleaner and probably a simpler convention to
>> clear the state when the buffers are being freed.  If there's a good
>> reason not to do this for igb, it makes me wonder if this should be
>> done the same way in other drivers...
>> 
>> Tom
> 
> Just dug up the old thread. This was to fix a bug that byte queue limits
> was causing with some of the loopback tests evoked from ethtool. The
> loopback test uses a separate path to free the buffers which wasn't
> calling netdev_tx_reset_queue().
> 
> We should likely just explicitly clear the state in each routine rather
> than try to be clever IMO.

Agreed.
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