From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: RE: Strange latency spikes/TX network stalls on Sun Fire
 X4150(x86) and e1000e
Date: Wed, 30 May 2012 13:04:55 +0200
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Cc: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>,
	Tom Herbert <therbert@google.com>,
	Denys Fedoryshchenko <denys@visp.net.lb>,
	netdev@vger.kernel.org, e1000-devel@lists.sourceforge.net,
	jeffrey.t.kirsher@intel.com, jesse.brandeburg@intel.com,
	davem@davemloft.net
To: David Laight <David.Laight@ACULAB.COM>
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On Wed, 2012-05-30 at 11:52 +0100, David Laight wrote:
> > > +	num_queued = dql->num_queued;
> > 
> > 
> > I suggest :
> > 
> > 	num_queued = ACCESS_ONCE(dql->num_queued);
> > 	
> > Or else compiler is free to do whatever he wants.
> 
> Or make the structure member volatile, then the
> compiler can only read it once.

No. Compiler can read it several times. Really.

> Probably worth while if the value is expected to
> be read like that.

Please don't use lazy volatile.

Unless you really want Linus flames (and ours)

ACCESS_ONCE() is much cleaner.