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From: Robert Watson <rwatson@FreeBSD.org>
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To: Gabor PALI <pgj@FreeBSD.org>
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Cc: svn-src-head@freebsd.org
Subject: Re: svn commit: r209119 - head/sys/sys
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On Fri, 9 Jul 2010, Gabor PALI wrote:

> On 06/18/10 14:08, Robert Watson wrote:
>> The only reservation I have, really, is that 64-bit writes are
> non-atomic on
>> i386 and other 32-bit architectures (or, at least, I think they are).
> This
>> means DPCPU_SUM may encounter non-atomicity rather than just staleness
> in the
>> values it reads as it iterates. That said, we should probably use 64-bit 
>> anyway, because 32-bit counters are gauche. :-)
>
> What is about introducing 64-bit atomic counters?

There's no native 64-bit atomic add primitive on most 32-bit platforms; 
however, I think I have an e-mail in my in queue from you suggesting an 
alternative approach that I haven't yet gotten to due to utter saturation 
here.  I assume there are reasonable alternatives that work around the 
potential race with a small probability of a missed or extra update, or 
similar, which would be fine.

Robert