Intel C2D COREs not used equally in FreeBSD 7.0-CURRENT i386

Oliver Fromme olli at lurza.secnetix.de
Tue Jun 5 13:16:45 UTC 2007


Abdullah Ibn Hamad Al-Marri wrote:
 > Jeff Roberson wrote:
 > > CORE is no longer supported and has been removed from the tree.  If you
 > > would like to try something new you can cvsup to sources from tonight and
 > > apply this patch:
 > > 
 > > http://people.freebsd.org/~jeff/schedsmp.diff
 > > 
 > > Then use options SCHED_SMP, which is a ULE variant.  Please report back
 > > your findings if you do try this.  However, it only works on amd64.
 > 
 > I can't wait for it if it's for i386. ;)
 > 
 > Would you implement it for i386 in the future too, or it's exclusive
 > for AMD64? :)
 > 
 > I don't have 4 GB ram, and I don't see a strong reason to switch to
 > AMD64 with 2 GB of ram,

It's a common mistake to assume that amd64 only makes sense
if you have >= 4GB RAM.  There are several reasons why it
might be useful to switch from i386 to amd64:

 - Most programs (though not all) will run faster, because
   in amd64 mode there are twice as many general-purpose
   registers, giving compilers much better opportunities
   for optimizations and caching of values, and reducing
   slow memory accesses.

 - Programs that use a lot of "long" values (64bit) will
   run faster because the processor can handle them
   natively.  In i386 mode those values have to be split
   into two 32bit parts, reducing performance noticeably.

 - Some applications might benefit from a larger virtual
   address space > 4 GB.  (Note that this is not related
   to the amount of physical RAM!)

 > beside 95% of the ports are 32bits even they
 > can run in AMD64.

I'm not sure I understand that sentence correctly, but
every possible interpretation is complete nonsense.

First, ports are neither 32bit nor 64bit, except for
binary ports, but that's a small minority.  Once you
build a port, it becomes either a 32bit binary or a
64bit binary, depending on the architecture on which
you build it.

Second, my guess is that > 95% of the ports are 64bit-
clean and will run on amd64 as native 64bit binaries.

In practice there's (almost) only one reason not to run
FreeBSD/amd64 on amd64-capable hardware:  If you depend
on a certain piece of software which is known not to run
correctly in 64bit mode.  Fortunately those are not many.

Best regards
   Oliver

-- 
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
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'Instead of asking why a piece of software is using "1970s technology,"
start asking why software is ignoring 30 years of accumulated wisdom.'


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