linux-kernel - Re: Why do we still have 32 bit counters? Interrupt counters overflow within 50 days

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Message-ID: <1412553572.11091.29.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sun, 05 Oct 2014 16:59:32 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Christoph Lameter <cl@...ux.com>,
	Richard Cochran <richardcochran@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Why do we still have 32 bit counters? Interrupt counters
 overflow within 50 days

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.



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