Date: Mon, 6 Oct 2014 09:54:14 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Eric Dumazet <eric.dumazet@gmail.com>
cc: Christoph Lameter <cl@linux.com>,
        Richard Cochran <richardcochran@gmail.com>,
        linux-kernel@vger.kernel.org
Subject: Re: Why do we still have 32 bit counters? Interrupt counters overflow
 within 50 days
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On Sun, 5 Oct 2014, Eric Dumazet wrote:
> On Sun, 2014-10-05 at 23:49 +0200, Thomas Gleixner wrote:
> 
> > Whats so hard about 64bit counters on 32bit machines?
> 
> Not hard, but not trivial either.
> 
> > 
> > > expensive to handle in particular because these counters are used in
> > > performance critical hotpaths.
> > 
> > The expensive overhead is a single "adcl" instruction.
> > 
> 
> Assuming a reader do not care of reading garbage yes, while carry is not
> yet propagated.

Readers and writers are serialized via desc->lock.

Thanks,

	tglx
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