amd64 webpage, 12GB memory? 64-bit or not? SMP or not?

Astrodog astrodog at
Sat Mar 18 18:14:07 UTC 2006

Processor feature flags are well documented. No need to duplicate work there.

As far as your system goes... it support Hyperthreading (Feature flag
HTT), so there's no good answer to your question. HTT doesn't seem to
have muc h effect one way or another on FreeBSD... though your system
does support it.

As far as taking ADVANTAGE of "options SMP", in your case, we can't
tell, its app by app. If you don't know if your system has 2 physical
cores or not, though, frankly, you have no business administrating it.
Well, that, and dmesg, and the bios will tell you.

I'm not sure I see the exact problem here.

--- Harrison Grundy

On 3/19/06, Jeremy C. Reed <reed at> wrote:
> Thank you, Joseph and Scott. I am replying to both Joseph's and Scott's
> emails below. (Plus I have new questions below :)
> On Sat, 18 Mar 2006, Joseph Vella wrote:
> > In the upper left part of the website homepage, there's a single
> paragraph.
> > The last sentence of that paragraph has a direct link to the page you
> refer.
> Thanks. I overlooked that. I was looking in the various lists of
> hyperlinks. Maybe the "amd64" could be hyperlinked above? (But then again
> maybe hyperlinking everything becomes too cluttered.) But I feel it should
> be hyperlinked for sure direct from the "Get FreeBSD" webpage.
> > Right after the lines you posted I have "Multiprocessor System Detected: 2
> > CPUs":
> ...
> > I had to recompile my kernel to get that.  I found it pretty easy to do,
> the
> > Handbook tells you how.  I'm not sure if this was in there but I had to
> add
> > "Options SMP"  to my kernel config file.
> That is my point. I do not want to compile and reboot with new kernel
> to know this. I am not asking how to get SMP enabled. I just want to know
> if this system even supports it.
> (Thanks for links to kernconfig.html and handbook. I have had the
> opportunity to read most of the handbook -- plus several other BSD books
> in addition to my own *BSD courseware -- already. And I have configured
> and built FreeBSD kernels hundreds of times, including many with SMP
> support.)
> I am looking for something like: "This machine appears to have support for
> multiprocessors; enabling 'options SMP' may take advantage of this."
> > The 'LM' string in the AMD Features lines tells you that it can go into
> long
> > mode, which means that it can operate in 64 bit mode.
> Awesome! That was what I was hoping. It would be great if this was listed
> somewhere, maybe on a FAQ or amd64 or i386 webpage. (If I overlooked this
> I am sorry, but please point me to it.) (I did find brief note of this in
> identcpu.c code, but that seems like the wrong way to find out and is
> not clear.)
> > > I understand. I know it is running GENERIC as I mentioned. My question
> is:
> > > How can I tell if it can take advantage of "options SMP" (from looking
> at
> > > 6.0-RELEASE i386 GENERIC output)?
> > >
> >
> > How can I tell if my car takes diesel or unleaded?  I'm sorry, but this
> > questioning sounds a bit hysterical.  But, if you truly have no other
> > way of knowing, compile and run the tool in /usr/src/tools/tools/ncpus.
> I don't know why it is funny. (Anyways with most cars, even without access
> to engine, you can look on dash board and on fuel cap and see.)
> Imagine someone giving you remote access to a system and you don't know
> what hardware it has (since you can not physically inspect). Rebooting
> with an SMP kernel seems like the slow way to find out. I am just curious
> if there is some way without rebooting, maybe the non-SMP kernel could
> detect and printf at boot time (for dmesg) something like: "It appears
> this system is multiprocessor; using 'options SMP' may be useful."
> I have used the ncpu's tool before (ported from FreeBSD to DragonFly). I
> didn't realize that it could tell a non-SMP kernel user about their
> multiprocessors.
> I didn't have a chance to run it yet on FreeBSD 6.0-RELEASE, as it does
> not compile:
> In file included from biosmptable.c:37:
> /usr/include/machine/mptable.h:143: error: syntax error before "pcib"
> Maybe because device_t is not defined yet. It is defined in sys/bus.h but
> only if _KERNEL.
> I will look at that later.
> It would be useful for a user to know if system is multiprocessor without
> building and running an outside tool (in this case not even included with
> FreeBSD 6.0-RELEASE).
> > > I have been looking at src/sys/i386/i386/identcpu.c. But I am not sure
> how
> > > an 64-bit Intel Xeon would behave. (I am guessing it would be
> CPUCLASS_686.)
> >
> > CPUCLASS_686 refers to Pentium Pro and above CPUs, and significantly
> > predates the 64-bit x86 architecture.  But fwiw, the i386 sources files
> > are not a good place to find 64-bit code.
> Understood. The system is running FreeBSD-6.0-RELEASE i386 GENERIC.  It
> would be interesting to add to the dmesg output: "Consider using the
> 'amd64' kernel" if that is appropriate.
> > > I do see that my dmesg output has AMD featuress with "LM" which means
> 64-bit
> > > long mode. But I don't know if that means this is a 64-bit system.
> >
> > YES!
> ...
> > > I am hoping the system I am looking at can run the amd64 kernel.
> >
> > Yes, it sure can.
> That was the answer I am looking for! Thank you!
> I will now reboot with an amd64 kernel. (Hopefully with reboot all my 12
> GB of memory will be seen; I do understand there are some issues with big
> memory.)
> Can you please point me to the webpage that says it is okay to boot an
> amd64 kernel using a i386 (6.0-RELEASE in this case) userland? (I will
> update userland after reboot.)
> Also can you point me to the documentation for cross-compiling amd64
> kernel and userland (on i386 host).
> The point of my email: it would be nice if there was some documentation or
> webpage or kernel boot output that can suggest to an i386 user that they
> should consider using an amd64 kernel instead -- and it would be nice if
> there was some documentation or webpage or kernel boot output that can
> suggest to a user that an "options SMP" kernel could be beneficial.
> Booting an amd64 kernel on a (possibly) non-amd64 system seems like the
> wrong way to find out.
> Booting an "options SMP" kernel to find out if multiprocessor seems like a
> slow way to find out.
> I will submit a patch for the amd64 webpage and maybe the FAQ and maybe
> the i386 webpage. Please review the following:
>   "If you boot with an i386 kernel and it shows an "AMD Features" line
>   containing an "LM" string, then you are operating in 64-bit long mode
>   and can use an amd64 kernel."
> (I don't have text for my SMP question since I still do not know the
> answer.)
> Thanks again for the replies.
>  Jeremy C. Reed
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