Date: Fri, 9 Jul 2010 19:50:29 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Gabor PALI <pgj@FreeBSD.org> Cc: svn-src-head@freebsd.org Subject: Re: svn commit: r209119 - head/sys/sys Message-ID: <alpine.BSF.2.00.1007091949170.94277@fledge.watson.org> In-Reply-To: <4C376B0E.9050505@FreeBSD.org> References: <4C376B0E.9050505@FreeBSD.org>
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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
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