FWIW, linux has had the capability to patch itself at boot, replacing slow instructions with fast ones (article mentions memory-barriers and "mfence" on newer CPUs)
http://lwn.net/Articles/164121/ SMP alternatives [Posted December 14, 2005 by corbet] so it may be that a 64bit kernel is just a 32bit kernel that can patch itself up to run fast on 64bit machines. On Wed, May 15, 2013 at 9:22 AM, David Ruggiero <thatseattle...@gmail.com>wrote: > On Mon, May 13, 2013 at 5:35 PM, Kyle Brantley <k...@averageurl.com> > wrote: > > In short, as per Intel, using the 6501 in a 64-bit mode is unsupported. > With that said, I've been > > running my 6501s in 64-bit mode exclusively, ever since I got one (two > weeks after release?). > > I've not had any problems with them, but then again, I may not be using > them in a way > > that triggers issues, should there be any. > > > A few months ago I asked the question here about what the pros and > cons would be of running the OpenBSD SMP kernel (bsd.mp) on the > net6501, versus the standard uniprocessor kernel - seeing that the > E6XX series has HyperTransport and therefore something approximating > multiple cores. There wasn't, as I recall, any consensus, or even much > information at all (*). So from this discussion, as far as I can tell, > I have a choice of _four_ different OpenBSD kernels that could > legitimately be booted on my net6501 and would probably run: > > 32-bit i386 uniprocessor > 32-bit i386 SMP > 64-bit amd64 uniprocessor > 64-bit amd64 SMP > > I'm sure a similar list of possible alternatives exists for other BSD > variants and for Linux. > > A different company than Soekris might do some quick testing, or at > least provide some pithy engineering insight and give its customers a > quick rundown from their point of view on the advantages and > disadvantages of 32 vs 64bit and non-smp vs smp - whether in general, > or for specific common application needs. But at the risk of being > flamed here, I'll say that I'm not holding my breath for any > information like that from the company anytime soon... > > If anyone has data points around these questions from actual personal > experience and actual real-world testing, like Kyle's, I'm sure many > would be grateful for that. > > D > > > (*) beyond the knowledge that "pf" is still single-threaded, so if all > you're using the box for is a packet filter/router, then smp won't > help _that_ particular much > _______________________________________________ > Soekris-tech mailing list > Soekris-tech@lists.soekris.com > http://lists.soekris.com/mailman/listinfo/soekris-tech >
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