netdev - Re: [net-2.6 PATCH 2/3] ixgbe: Fix tx_restart_queue/non_eop

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Date:	Sun, 13 Dec 2009 20:57:05 -0800
From:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
To:	David Miller <davem@...emloft.net>
Cc:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"Chilakala, Mallikarjuna" <mallikarjuna.chilakala@...el.com>
Subject: Re: [net-2.6 PATCH 2/3] ixgbe: Fix tx_restart_queue/non_eop_desc
 statistics counters

On Sun, 2009-12-13 at 19:18 -0800, David Miller wrote:
> From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> Date: Fri, 11 Dec 2009 23:51:41 -0800
> 
> > @@ -4528,10 +4529,12 @@ void ixgbe_update_stats(struct ixgbe_adapter *adapter)
> >  
> >  	/* gather some stats to the adapter struct that are per queue */
> >  	for (i = 0; i < adapter->num_tx_queues; i++)
> > -		adapter->restart_queue += adapter->tx_ring[i].restart_queue;
> > +		restart_queue += adapter->tx_ring[i]->restart_queue;
> > +	adapter->restart_queue = restart_queue;
> 
> I don't see how these two versions of the code can behave
> differently unless there is very broken locking on the
> adapter->* statistic counters.

The problem is the adapter->restart_queue is being double-counted.  If
we accumulate from each ring's restart_queue, which are cumulative, then
we don't want to add it to the previous update_stats() values in
adapter->restart_queue.

> I'm not applying this without at least a better commit
> log message.

We can fix the commit log message to better explain what the problem is.

Thanks,
-PJ

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