netdev - RE: [PATCH net v4 3/4] r8152: support stopping/waking tx queue

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Date:	Wed, 20 Nov 2013 14:30:56 +0800
From:	hayeswang <hayeswang@...ltek.com>
To:	'David Miller' <davem@...emloft.net>
CC:	<netdev@...r.kernel.org>, 'nic_swsd' <nic_swsd@...ltek.com>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: RE: [PATCH net v4 3/4] r8152: support stopping/waking tx queue

 David Miller [mailto:davem@...emloft.net] 
[...]
> > If the situation occurs, it means there is no tx buffer at 
> that time. If the
> > netif_wake_queue() is called, only one more packet would be 
> queued and the tx
> > queue would be stopped again after calling 
> rtl8152_start_xmit(). That is, it
> > is not necessary to wake the queue. Besides, after the tx 
> is completed, another
> > tasklet would be scheduled if there is any packet which is 
> queued in the list.
> > That is, the r8152_tx_agg_fill() would be called and the 
> netif_queue_stopped()
> > would be check againg, so the tx queue would not be stopped forever.
> 
> Then the queue can be woken when in fact r8152_start_xmit() 
> is not able to
> actually queue packets.  It is just as equally problematic.
> 
> You have to synchronize this state, somehow.
> 
> tg3 driver does this by taking netif tx queue lock during the wake
> test sequence in TX reclaim.  This works because ->ndo_start_xmit() is
> run with this lock held.

Thanks for your answer. I would modify it.

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